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LIBRARY 

OF   THE 

UNIVERSITY  OF  CALIFORNIA. 


MONOGRAPHS 

ON 

APPLIED  ELECTROCHEMISTRY 

EDITED  BY 

VIKTOR  ENGELHARDT, 

Head  Engineer  and  Chief  Chemist  of  the  Siemens  &  Halske  A.  G. , 

Vienna. 

WITH  THE  COOPERATION  OF 
Dr.  E.  Abel,  Chemist  for  the  Siemens  &  Halske  A.  G.,  Vienna. 

E.  G.  Acheson,  President  of  the  International  Acheson  Graphite  Co., 

Niagara  Falls,  N.  Y. 

Dr.  P.  Askenasy,  Superintendent  of  the  Akkumulatorwerke,  Liesing. 

H.  Becker,  Publisher  of  "L'Industrie  electro-chimique, "  Paris. 

Dr.  W.  Borchers,  Professor  at  the  Technical  High  School,  Aachen. 

Sh.  Cowper-Coles,  Publisher  of  "The  Electrochemist  and  Metallur- 
gist," London. 

Dr.  F.  Dieffenbach,  Professor  at  the  Technical  High  School,  Darm- 
stadt. 

Dr.  G.  Erlwein,  Chief  Chemist  of  the  Siemens  &  Halske  A.  G.,  Berlin. 

H.  Friberg,  Engineer  of  the  Siemens  &  Halske,  A.  G.,  Berlin. 

H.  Gall,  Director  of  the  Socie"te  d'Electrochimie,  Paris. 

F.  E.  Giinther,  Mining  Engineer,  Aachen. 

Dr.  F.  Haber,  Professor  at  the  Technical  High  School,  Karlsruhe. 

Dr.  C.  Ha'ussermann,  Professor  at  the  Technical  High  School,  Stutt- 
gart. 

Dr.  R.  Hammerschmidt,  Electrochemist,  Charlottenburg. 

Dr.  G.  Hausdorff,  Registered  Chemist,  Essen. 

Dr.  K.  Kellner,  General  Director,  Vienna. 

A.  Krakau,  Professor  of  the  Electrochemical  Institute,  St.  Petersburg. 

Dr.  H.  Landolt,  Director  of  the  Society  for  Electrochemical  Industry, 
Turgi. 

Dr.  M.  Le  Blanc,  Professor  at  the  Technical  High  School,  Karlsruhe. 

C.  Liebenow,  Engineer,  Berlin. 

Dr.  R.  Lorenz,  Professor  at  the  Swiss  Polytechnic,  Zurich. 

Dr.  R.  Lucion,  Director  of  Solvay  &  Co.,  Brussels. 

A.  Minet,  Publisher  of  "  L'l^lectrochimie,  "  Paris. 

A.  Nettel,  Engineer,  Berlin. 

H.  Nissenson,  Director  of  Akt.-Ges.  of  Stolberg  &  Westfalen, 
Stolberg. 

Dr.  F.  Peters,  Instructor  at  the  Royal  Mining  Academy,  Berlin. 

Dr.  W.  Pfanhauser,  Manufacturer,  Vienna. 

Registered  Chemist  Dr.  O.  Prelinger,  Chemist  of  the  Siemens  & 
Halske  A.  G.,  Vienna. 

Titus  Ulke,  M.  E.,  Electrometallurgical  and  Mining  Engineer  of  the 
Lake  Superior  Power  Co.,  Sault  Ste.  Marie,  Ontario. 

Dr.  Th.  Zettel,  Chief  Chemist  of  Brown-Boveri  &  Co,,  Baden. 
And  other  experts. 


MONOGRAPHS    ON    APPLIED     ELECTROCHEMISTRY. 

VOL   III. 


THE  PRODUCTION  OF 

Chromium  and  Its  Compounds 

BY  THE  AID  OF  THE 

Electric  Current 

BY 

DR.  MAX  LE  BLANC. 


PROFESSOR    AND    DIRECTOR    OF    THE    PHYSICAL-CHEMICAL 

(ELECTROCHEMICAL)  INSTITUTE  OF  THE  TECHNICAL 

HIGH  SCHOOL,    KARLSRUHE. 


AUTHORIZED  ENGLISH  TRANSLATION  BY 

JOSEPH  W.  RICHARDS,  M.A.,  A.C.,  PH.D. 

PAST-PRESIDENT  OF  THE  AMERICAN  ELECTROCHEMICAL,  SOCIETY. 
PROFESSOR  OF  METALLURGY  AT  LEHIGH  UNIVERSITY. 

[^  or  THE 
f  UNIVERSITY 

PUBLISHED   BY   THE   CHEMICAL    PUBLISHING   COMPANY, 
1904. 


~r~P 


7  " 

Itni 


COPYRIGHT,  1904,  BY  THE  CHEMICAL  PUBLISHING  Co. 


AUTHOR'S  PREFACE  TO  THE  GERMAN  EDITION. 

It  has  been  my  endeavor  to  give  in  the  present  Monograph 
a  complete  review  of  what  has  been  published  up  to  the  end  of 
the  year  1901,  in  relation  to  the  manufacture  of  chromium  and 
its  compounds  with  the  assistance  of  the  electric  current. 
To  accomplish  this  I  undertook  a  comprehensive  study  of  the 
literature  of  the  subject,  in  particular  reviewing  the  German, 
English  and  American  patent  literature.  I  can  scarcely  hope 
to  attain  the  end  I  had  in  view,  since  to  get  together  all  the 
observations  which  have  been  made  concerning  chromium, 
part  of  which  are  in  places  where  they  would  scarcely  be  ex- 
pected, is  indeed,  at  least  for  the  single  investigator,  an  almost 
impossible  task ;  I  may,  however,  remark  that  I  have  taken 
special  pains  in  this  direction.  I  shall  receive  with  thanks 
any  information  concerning  items  which  I  have  overlooked 
and  which  are  deserving  of  mention. 

The  original  publications  quoted  have  been  extracted  in 
such  manner  that  reference  to  the  original  for  further  par- 
ticulars is  in  most  cases  unnecessary.  Further  remarks  on 
this  subject  are  made  on  page  10. 

It  will  be  to  me  a  satisfaction  if  this  work  proves  itself  of 
service  to  my  colleagues  in  the  profession. 

I  thank  heartily  Dr.  J.  Erode  for  his  friendly  assistance  in 
reading  the  proof.  M.  LE  BLANC. 

Karlsruhe. 


TRANSLATOR'S    PREFACE. 

The  study  of  these  attempts  to  produce  chromium  and  its 
compounds  electrolytically  will  be  profitable  not  only  to  the 
electrochemist  particularly  interested  in  chromium,  but  also 
to  every  active  electrochemist  whose  work  deals  with  difficult 
problems  in  electrolysis. 

I  wish  to  acknowledge  the  assistance  furnished  by  Walter 
S.  Landis,  Met.  Eng.,  in  the  preparation  of  the  manuscript 
and  reading  of  proofs.  JOSEPH  W.  RICHARDS. 

Lehigh  University. 


.A   O  O 


CONTENTS. 


I.  OBTAINING  OF  METALLIC  CHROMIUM  ....  i 

A.  By  electrolysis  of  aqueous  solutions  .    '. I 

B.  By  the  use  of  high  temperatures 32 

II.  THE  OBTAINING  OF  COMPOUNDS   OF   CHRO- 
MIUM WITH  METALS 53 

A.  By  electrolysis  of  aqueous  solutions 53 

B.  By  the  use  of  high  temperatures 54 

III.  OBTAINING  OF  THE  COMPOUNDS  OF   CHRO- 
MIUM WITH  THE  NON-METALS 66 

A.  Carbon  compounds 66 

B.  Silicon  compounds 67 

C.  Phosphorus  compounds 71 

D.  Sulphur  compounds 72 

E.  Oxygen  compounds 73 

(1)  Chromous  oxide  compounds 73 

(2)  Chromic  oxide  compounds 76 

(fl)  BY  ELECTROLYSIS  OF  AQUEOUS  SOLUTIONS  76 

(b)  BY  THE  USE  OF  HIGH  TEMPERATURES     .     .  8 1 

(3)  Chromic  acid  compound 86 

(a)  CHROMATES  OF  THE  HEAVY  METALS  ...  86 
(£)  CHROMATES  OF  THE  ALKALI  METALS  AND 

CHROMIC  ACID 95 

APPENDIX  ....  .120 


I.    OBTAINING  OF  METALLIC  CHROMIUM. 


A.   By  Electrolysis  of  Aqueous  Solutions. 

Nearly  fifty  years  ago  Bunsen,  in  his  ramblirigs  in  the  field 
electrochemistry,  found  a  process  for  the  manufacture  of  me- 
tallic chromium.1  At  that  time  the  cheap  production  of 
chemical  compounds  on  a  large  scale  with  the  assistance  of 
the  electric  current  was  essentially  impracticable,  and  it  has 
only  been  in  the  last  fifteen  years,  in  fact,  that  the  previously 
unanticipated  development  of  electro-technology  has  rendered 
it  possible.  I  reproduce  the  most  important  principles  of  his 
manipulation,  mostly  in  his  own  words,  which  show  an  aston- 
ishing clearness  of  view  considering  the  time  at  which  it  was 
written,  concerning  the  importance  of  current  density  in  elec- 
trolytic operations. 

"  Most  important  for  the  chemical  action  of  the  current  is 
the  density  of  the  current,  that  is,  the  current  strength  divided 
by  the  electrode  surface  at  which  the  electrolysis  takes  place. 
With  this  density  increases  the  power  of  the  current  to  over- 
come the  chemical  affinities.  If  one  conducts  a  current,  for  in- 
stance, of  constant  strength  through  a  cell  of  chromic  chloride 
in  water,  it  depends  upon  the  area  of  the  reducing  electrode 
whether  one  gets  hydrogen,  chromic  oxide,  chromous  oxide? 
or  metallic  chromium.  The  relative  amounts  of  the  constit- 
uents of  the  electrolyte  through  which  the  current  passes 
are  of  no  less  importance.  If  one  increases  gradually,  for 
instance,  the  amount  of  chromous  chloride  in  solution,  keep- 
ing constant  the  current  strength  and  the  electrode  surfaces, 
a  point  is  soon  reached  where  the  elimination  of  chromous 
oxide  is  accompanied  by  a  reduction  of  the  metal  and  finally 
is  entirely  replaced  by  it." 

He  then  describes  further  on  the  decomposing  cell,  one  pole 
of  which  was  the  interior  surface  of  a  carbon  crucible  con- 
tained inside  a  porcelain  crucible  and  filled  with  hydrochloric 
acid,  and  kept  hot  in  a  water-bath,  while  the  other  pole  was 

1  Poggendorff's  Ann.  91,  619  (1854). 


2  CHROMIUM  AND  ITS  COMPOUNDS 

a  narrow  strip  of  platinum  placed  inside  a  clay  cell  in  which 
the  fluid  to  be  decomposed  was  placed,  and  the  whole  stood 
inside  the  carbon  crucible.  This  arrangement  proved  itself 
as  very  suitable  for  the  obtaining  of  high  current  densities  at 
one  electrode,  and  he  recommended  it  in  general  for  the 
electrolytic  deposition  of  metals,  especially  for  the  reduction 
of  chromium  from  its  aqueous  solutions. 

"  Using  in  such  a  reduction  experiment  chromous  chloride 
solution  containing  some  chromic  chloride,  metallic  chromium 
can  be  easily  obtained  in  continuous  sheets  of  50  sq.  mm.  in 
size,  but  quite  brittle,  the  surface  lying  against  the  platinum 
electrode  being  perfectly  white  and  of  metallic  lustre.  The 
chromium,  which  can  be  obtained  chemically  pure  only  in 
this  way,  resembles  iron  very  much  in  its  external  appear- 
ance, but  it  is  more  permanent  in  damp  air  and  burns  on  being 
heated  in  air  to  chromic  oxide.  Hydrochloric  and  sulphuric 
acids  dissolve  it  slowly  to  chromous  salts  with  evolution  of 
hydrogen.  It  is  scarcely  attacked  by  nitric  acid  even  when 
boiling." 

Bunsen  gives  further  details  of  the  experiments  in  the  fol- 
lowing sentences:  "The  reduction  of  the  metal  takes  place 
therefore  out  of  concentrated  chlorous  solutions  heated  to 
boiling,  when  each  square  millimeter  of  the  reducing  pole 
surface  receives  a  current  of  the  absolute  intensity  0.067. z  •  •  • 
If  the  current  density  is  gradually  lowered  a  point  is  soon 
reached  where  the  reduction  of  metal  disappears,  and  is  re- 
placed by  a  copious  formation  of  anhydrous  chromous-chromic 
oxide.  This  oxide  can  be  made  only  in  this  manner  and  can 
be  made  in  large  quantities  and  is  purified  by  long  boiling 
with  aqua  regia.  It  is  a  very  black  non-crystalline  powder, 
soluble  in  no  acid,  and  burning  in  the  air  like  pyrophoric 
iron,  with  lively  deflagration,  to  a  green  chromic  oxide.  The 
composition  of  this  chromous-chromic  oxide  varies  between 

Cr2Cr    and    Cr3Cr"  (Cr4O5  and   CrsO6.      See  further    under 

1  0.67  ampere  per  square  centimeter. 
r    "^  sa*AAJA      UA>V  CA       C/H*        %V\l 

*" 


BY   ELECTROLYSIS   OF   AQUEOUS   SOLUTIONS.  3 

chromic  oxide)."  Bunsen  remarks  finally  that  it  would  cer- 
tainly be  of  great  interest  to  prove  whether  the  metal  reduced 
out  of  the  green  and  the  blue  salts  of  chromium  is  identical 
in  both  cases,  or  u  whether  the  allotropic  conditions  would 
make  themselves  evident  also  in  the  deposited  metal."  At 
present  we  recognize  as  the  ground  for  the  division  between 
the  green  and  the  blue  chromium  solutions,  the  presence  in 
them  of  different  molecules  or  molecular  complexes,  and  no 
longer  speak  of  the  allotropic  form  of  the  metal  in  these  two 
solutions.1 

The  data  of  Bunsen  are  on  the  one  hand  valuable  for  the 
general  point  of  view  which  they  take,  and  for  the  conditions 
which  they  impose  for  the  separation  of  chromium,  but  one 
misses  on  the  other  hand  exact  numercial  data  ;  his  work  has 
the  appearance  as  if  he  had  left  over  for  a  more  comprehen- 
sive work  the  determination  of  the  exact  details,  as  is  indi- 
cated by  the  following  sentence:  "  I  have  so  far  determined 
the  influences  on  which  the  decomposing  power  of  the  current 
depends,  and  have  left  over  further  investigations  to  my  stu- 
dents." However,  nothing  further  on  the  subject  was  pub- 
lished. 

The  next  investigations  on  the  obtaining  of  chromium  were 
a  generation  later  ;  they  were  directed  towards  the  industrial 
manufacture  of  chromium  and  are  part  of  patent  literature. 
The  names  of  Placet  and  Bonnet  are  in  particular  found  at 
the  heads  of  such  patents  which  were  concerned  principally 
with  the  electrolysis  of  metallic  compounds  in  general,  and 
partly  in  particular  with  the  electrolytic  production  of  chro- 
mium. We  will  consider  the  contents  of  the  first  as  far  as  it 
refers  to  chromium. 

The  first  patent  of  these  two  experimenters  is  concerned 
with  improvements  in  electrolysis  in  general,  and  in  particular 
with  the  electrolysis  of  metallic  solutions.2  It  is  characterized 
like  others  of  their  patents  by  its  comprehensiveness,  by  its  very 

1  R.  Whitney  :   Zeitschr.  f.  physik.  Cheuiie,  2O,  40  (1896). 

2  English  Patent  No.  19, 344, November  27,  1890. 


4  CHROMIUM  AND  ITS  COMPOUNDS. 

general  point  of  view  and  by  its  endeavor  to  extend  the 
limits  of  the  patent  as  far  as  possible. 

They  ascribe  the  poor  results  in  the  electrolytic  separation 
of  metals,  up  to  their  time,  to  the  injurious  formation  of  gas 
bubbles  on  the  negative  electrode.  In  order  to  prevent  this 
they  recommend  keeping  the  bath  under  an  increase  or  de- 
crease of  pressure  ;  if  this  is  done,  then  can  all  metals — chro- 
mium is  particularly  named — be  obtained  electrolytically 
with  the  greatest  ease,  of  high  purity  and  of  any  desired  size 
and  thickness,  by  simply  using  high  current  density  !  Satis- 
factory results  are  also  said  to  be  obtained  by  taking  two 
electrodes  of  different  conductivity,  for  instance  a  copper  wire 
for  leading  in  the  electricity  to  the  cell  and  an  iron,  zinc 
or  platinum  electrode  for  the  taking  away  of  the  current. 
Or  two  electrodes  may  be  used  of  the  same  material  but  of 
different  sizes.  In  place  of  the  increasing  of  the  external 
pressure  similar  good  results  may  be  obtained  in  many 
cases  by  increasing  the  density  of  the  bath  by  dissolv- 
ing in  it  salts  of  more  electropositive  metals.  The  following 
salts  are  recommended  for  this  purpose  :  i.  Saturated  solution 
of  a  mixture  of  potassium,  sodium  and  ammonium  sulphates ; 
2.  Saturated  solution  of  a  mixture  of  potassium,  sodium  and 
ammonium  chlorides  ;  3.  Saturated  solution  of  the  sulphate 
or  chloride  of  the  metal  to  be  deposited. 

A  litre  each  of  the  three  solutions  is  taken  and  mixed  ;  this 
mixture  is  a  remarkable  bath  from  which  the  metal  can  be 
precipitated  pure  in  any  desired  thickness! 

In  place  of  the  saturated  solutions,  normal  concentrated 
solutions  may  be  taken,  120  to  150  grams  of  each  of  the  three 
alkaline  salts  and  150  to  200  grams  of  the  metallic  salt  to 
each  litre  of  water. 

For  the  refining  of  metals  a  mixture  is  recommended,  made 
by  pouring  together  a  litre  of  each  of  the  saturated  solutions 
of  the  three  alkaline  chlorides  and  three  alkaline  sulphates  as 
well  as  water  acidified  with  sulphuric  or  hydrochloric  acids. 


BY   ELECTROLYSIS   OF   AQUEOUS   SOLUTIONS.  5 

As  electrodes,  two  plates  of  the  metal  to  be  refined  are  used. 

The  alkaline  sulphates  and  chlorides  may  be  replaced  by 
all  other  possible  salts ;  by  alkaline  nitrates  and  phosphates, 
magnesium  chloride  and  nitrate,  etc.  According  to  the  nature 
of  the  metal  the  baths  should  be  alkaline,  neutral  or  acid  ; 
especially  with  chromium  they  should  be  strongly  acid. 

For  acidifying  the  baths  all  possible  organic  acids  may  be 
used  besides  the  inorganic.  The  addition  of  acid  influences 
favorably  the  purity  of  the  deposited  metal  since  any  acci- 
dental suboxide  will  be  dissolved.  Warming' of  the  solution 
appears  advantageous. 

Either  soluble  or  insoluble  anodes  may  be  used,  and  it  is 
recommended  to  use  diaphragms  in  order  to  avoid  polarizing 
action  by  gas  bubbles  and  the  contamination  of  the  bath  in 
consequence  of  insufficient  purity  of  the  anodes,  the  anodes 
being  immersed  in  fluids  which  will  combine  with  the  oxygen 
set  free  there,  for  instance  sulphuric  acid,  hydrochloric  acid, 
sodium  chloride  solution,  sulphurous  acid,  etc.  When  using 
insoluble  anodes,  polarization  may  be  largely  avoided  by 
roughening  their  surface. 

The  quality  of  the  precipitate  is  improved  by  the  addition 
(i  to  2  grams  to  10  litres)  of  all  possible  organic  compounds, 
such  as  gelatine,  gum,  etc.,  or  sulphur  chloride,  sodium  sul- 
phide, iodine,  arsenic  acid,  etc. 

To  obtain  alloys  the  following  procedure  is  recommended : 
After  making  the  bath  of  great  density,  for  instance,  the 
above-described  mixture  of  the  three  alkaline  sulphates  or 
chlorides,  there  is  added  the  salt  of  the  different  metals  which 
one  wishes  to  alloy,  or  soluble  anodes  of  the  metals  concerned 
are  used.  Then  a  feeble  current  is  passed  through  the  solu- 
tion and  gradually  increased.  Two  cases  are  now  possible. 
If  the  bath  is  acid,  that  metal  which  is  the  most  electronega- 
tive is  deposited  first ;  if  the  bath  is  alkaline,  that  metal  sepa- 
rates out  first  which  is  the  most  electropositive !  Later,  it  is 
stated,  that  it  is  only  necessary  to  increase  the  strength  of 
the  current  in  order  to  obtain  an  alloy  consisting  of  all  of  the 


6  CHROMIUM  AND  ITS  COMPOUNDS. 

metals  contained  in  the  bath.  The  relative  quantities  of  metal 
in  the  alloy  may  be  varied  by  altering  the  relative  concentra- 
tions or  the  surfaces  of  the  soluble  metallic  anodes. 

Operating  in  this  way  very  malleable  alloys  of  zinc,  tin  or 
copper  with  aluminium,  chromium,  tungsten,  and  molybdenum 
have  been  obtained,  also  very  hard  and  coherent  deposits 
of  chromium  with  tungsten,  iron  and  molybdenum,  and  very 
light  alloys  of  aluminium  with  a  small  quantity  of  chromium,, 
tungsten,  iron  and  molybdenum. 

If  the  ores  are  sufficiently  good  conductors  of  electricity 
they  may  be  used  directly  as  anodes.  In  other  cases  the  valu- 
able metals  must  be  dissolved  and  can  then  be  obtained  in  the 
vpure  condition  from  the  impure  salts  by  the  methods  de- 
scribed. 

We  reproduce  here  only  those  patent  claims  which  relate 
directly  or  indirectly  to  chromium  : 

(1)  A  method  of  strengthening  the  action  of  the  current  in 
electrolysis  consisting  in  subjecting  the  hot  or  cold  electrolyte 
to  a  determined  pressure,  obtained  either  by  physical   meansr 
gas  pressure  or  fluid  pressure,  or  by  a  greater  density  of  the 
electrolyte  obtained  by  dissolving  therein  indifferent  material 
not  decomposed   by  the  current,  or  by  using  conductors  of 
various  cross-section  or  various  conductivities,  which  hinder 
the  current  in  its  passage  and  so  produce  an  artifical  pressure. 

(2)  An  exerting  of  pressure  upon  the  hot  or  cold  electro- 
lytic bath  containing  the  compound  of  the  metal  to  be  depos- 
ited, or  in  which  the  anode  of  the  metal  concerned  is  placed. 
This   pressure   is  obtained  by  physical  means  (gas  or  fluid 
pressure),  and  at  the  same  time  currents  of  comparatively  high 
intensity  are  used  for  the  production  of  the  pure  metal. 

(3)  The  exerting  of  pressure  upon  the  hot  or  cold  electro- 
lytic bath  containing  different  compounds  of  two,  three  or 
more  metals  or  in  which  anodes  formed  of  these  metals  are 
dipped.     This  pressure  is  produced  by  physical  means,  and 
such  currents  are  utilized  at  the  same  time  whose  electromo- 
tive force  and  intensity  can  be  so  regulated  that  the  precipitate 


BY   ELECTROLYSIS   OF   AQUEOUS   SOLUTIONS.  7 

of  those  metals  is  obtained  of  which  the  alloy  should  consist. 

(4)  The  use  of  anodes  of  varying  section  and  different  con- 
ductivity as  the  means  for  the  production  of  the  artificial  cur- 
rent pressure,  using  at  the  same  time  a  current  of  relatively 
high  intensity,  the  electrolytic  bath  being  either  hot  or  cold 
and  containing  the  metal  or  metals  to  be  deposited. 

(5)  The  use  of  hot  or  cold  electrolytic  baths  whose  density 
and  consequently  the  pressure  is  increased  by  the  solution  of 
indifferent  salts  as  sulphates,  sulphites,  phosphates,  or  oxalates 
of  the  alkalies  or  alkaline  earths  and,  in  fact,  by  all  com- 
pounds of  all  bases   which  are  more  electropositive  or  more 
electronegative  than  the  metal  to  be  deposited  according  as  to 
whether  the  bath  is  acid  or  alkaline,  and  which  contain  the 
compounds  of  the  metal  to  be  deposited,  while  pure  or  impure 
soluble  anodes  of  the  metals  contained  in  the  bath  are  used, 
using  at  the  same  time  currents  of  relatively  high  intensity. 

(6)  The  use  of  cold  or  hot  electrolytic  baths  whose  density 
is  increased  by  saturating  them  with  (a)  the  three  alkaline 
sulphates,  (ft)  the  three  alkaline  chlorides,  (c)  a  sulphate  or  a 
chloride  or  a  soluble  compound  of  the  metal  to  be  deposited, 
using  at  the  same  time  currents  of  relatively  high  intensity. 

(7)  The  use  of  cold  or  warm  electrolytic  baths  whose  den- 
sity may  be  increased  by  preparing  them  from  saturated  solu- 
tions of  (a)  the  three  alkaline  sulphates,  (b)  the  three  alkaline 
chlorides,  in  which  are  placed  soluble  anodes  of  the  metals  to 
be  deposited,  using  at  the  same  time  currents  of  relatively 
high  intensity. 

(8)  The  use  of  electrolytic  baths  whose  density  is  increased 
by  making  them  from  a  saturated  solution  of  the  three  alka- 
line chlorides,  or  a  saturated  solution  of  the  three  alkaline 
sulphates  and  to  one  of  these  solutions  a  saturated  solution  of 
the  chloride  or  sulphate  of  any  other  soluble  salt  of  the  metal 
to  be  deposited  is  added,  or  by  using  smooth  or  rough  anodes 
of  the  metal  concerned,  using  at  the  same  time  currents  of  rela- 
tively high  intensity. 


8  CHROMIUM  AND  ITS  COMPOUNDS. 

(9)  The  use  of  electrolytic  baths  whose  density  is  increased 
as  described  above  and  which  contain  insoluble  anodes  placed 
in  porous  vessels,  which  latter  contain  for  the  avoidance  of 
polarization  one  of  the  following  solutions :  Sulphuric  acid, 
hydrochloric   acid,  sodium    chloride,   calcium   chloride,   sul- 
phurous acid  or  sulphites,  using  at  the  same  time  currents  of 
relatively  high  intensity. 

(10)  The  use  of  electrolytic  baths  whose  density  is  increased 
as  before  described  and  in  which  soluble,  roughened  anodes 
are  placed  in  porous  vessels  for  the  avoidance  of  polarization 
and  the  arrangement  of  which  is  shown  in  the  accompanying 
plate,  for  the  purpose  of  avoiding  the  contamination  of  the 
bath  by  the  impurities  of  these  anodes,  using  at  the  same  time 
currents  of  relatively  high  intensity. 

(n)  The  use  of  electrolytic  baths  whose  density  is  increased 
as  above  described  in  which  roughened  soluble  or  insoluble 
anodes  are  contained  in  porous  vessels  whose  arrangement  is 
shown  by  the  accompanying  plate  and  which  contains  a  de- 
polarizing fluid  in  case  insoluble  anodes  are  used.  The  de- 
polarization fluid  or  the  fluid  to  be  decomposed  or  both  should 
be  automatically  renewed,  using  at  the  same  time  currents  of 
relatively  high  intensity. 

(12)  The  use  of  electrolytic   baths   whose   density   is  in- 
creased as  above  described  in  which  a  soluble  zinc  anode  is 
placed  in  a  porous  vessel  containing  oxalic  acid  or  an  alkaline 
oxalate  in  order  to  hinder  the  zinc  salt  formed  from  passing 
into  the  bath  which  is  being  decomposed,  using  at  the  same 
time  currents  of  relatively  high  intensity. 

(13)  The  use  of  electrolytic  baths    whose    density   is  in- 
creased as  before  described,  into  which  a  soluble  or  insoluble 
anode  dips  and  in  which,  for  the  improvement  of  the  quality 
of  the  metal,  there  is  added  per  litre  of  bath  i  to  2  grams  of 
gelatine,  gum,  dextrin  or  similar  material,  using  at  the  same 
time  currents  of  relatively  high  intensity. 

(16)  The  use  of  electrolytic  baths  whose  density  is  in- 
creased as  before  described  and  into  which  dip  soluble  anodes 


BY    ELECTROLYSIS   OF   AQUEOUS   SOLUTIONS.  9 

(ores  when  of  sufficient  conductivity  may  be  used  as  anodes) 
or  in  which  compounds  of  the  metals  to  be  deposited  as  alloys 
are  dissolved  (these  compounds  may  be  the  ores  of  such 
metals  if  sufficiently  soluble).  The  surfaces  of  the  anodes 
and  the  relative  quantities  in  which  the  compounds  are  dis- 
solved vary  according  to  the  proportions  in  which  the  metals 
are  desired  in  the  alloys,  using  at  the  same  time  a  current 
whose  electromotive  force  and  intensity  may  be  so  regulated 
•that  a  precipitate  of  the  metals  is  obtained  of  which  the  alloy 
.should  consist. 

(17)  The  alloys:    (a)  of  aluminium,  zinc,  tin   or  copper, 
of  chromium,  zinc,  tin  or  copper,  of  tungsten,  zinc,  tin  or  copper, 
of  molybdenum,  zinc,  tin  or  copper,  etc.;  (d)  of  molybdenum  and 
silver,  of  uranium  and  silver  ;  (c)  of  chromium  and  tungsten, 
of  iron  and  chromium,  of  nickel  and  chromium,  of  nickel  and 
molybdenum,  etc.;  (d)  of  aluminium  and  chromium,  of  alu- 
minium and  tungsten,  of  aluminium  and  iron,  of  aluminium  and 
molybdenum,  etc.     These  alloys  can  be  alloyed  with  each 
other. 

(18)  The  use  of  electrolytic  baths  whose  density  is  increased 
as  before  described  and  in  which  good  conducting  ores  are 
used  as  soluble  anodes,  using  at  the  same  time  currents  of  rel- 
atively high  intensity  suitable  for  precipitating  the  metal. 

(19)  The  use  of  electrolytic  baths    whose  density  is    in- 
creased as  before   described  in  which  poorly  conducting  ores 
are  dissolved   by  being  previously  transformed  into  soluble 
sulphates,  chlorides,  etc.,  using  at  the  same  time  a  current  of 
relatively  high  intensity  suitable  for  precipitating  the  metal. 

(20)  The  use  of   electrolytic    baths  whose   density  is  in- 
creased as  before  described,  in  which  the  compounds  of  valu- 
able metals  are  dissolved,  in  case  these  are  soluble  or  trans- 
formable  into  soluble   compounds,  using  at  the  same  time 
currents  whose  density  may  be  progressively  altered  in  order 
to  precipitate  successively  the  single  metals  forming  the  alloys. 

(21)  The    use   of   electrolytic    baths  whose  density  is  in- 
creased as  before  described  and  in  which  the  alloys  of  valuable 


10  CHROMIUM  AND  ITS  COMPOUNDS. 

metals  dip,  if  these  alloys  can  serve  as  soluble  anodes,  using- 
at  the  same  time  a  current  whose  intensity  may  be  progres- 
sively altered  in  order  to  be  able  to  precipitate  successively  the 
single  metals  forming  the  alloy. 

(22)  The  use  of  several  electrolytic  baths  in  series  whose 
density  is  increased,  or  which  are  subjected  to  an  increased 
pressure  as  before  described,  and  in  which  one  or  more  me- 
tallic compounds  are  dissolved  or  in  which  one  or  more  solu- 
ble anodes  are  placed,  according  to  whether  a  single  metal  or 
alloy  is  to  be  produced,  using  at  the  same  time  currents  of 
relatively  high  intensity,  whose  intensity  and  electromotive 
force  may  be  altered  in  the  case  that  alloys  are  to  be  manu- 
factured. 

It  is  superfluous  to  criticize  the  above  patent  claims  since 
every  one,  who  has  only  a  small  knowledge  of  the  subject,  rec- 
ognizes at  once  that  these  are  not  the  outcome  of  actual  ex- 
periments, but  are  at  least  for  the  most  part  mere  fantasies. 
The  further  patents  of  Placet  and  Bonnet  contain  similar 
fantasies,  and  they  are  to  be  found  also  in  the  patents  of  other 
inventors.  An  explanation  of  this  lies  in  the  fact  that  the 
patent  specifications  are  often  written  out  before  the  comple- 
tion and  at  times  even  before  the  beginning  of  tedious  investi- 
gations, and  on  this  account  contain  statements  which  have 
in  no  way  been  controlled  by  experiment.  On  this  account  a 
certain  caution  is  to  be  recommended  concerning  statements 
in  patents. 

The  question  may  be  quite  prudently  asked  as  to  whether 
it  is  worth  while  to  reproduce  the  contents  of  such  fantastic 
patents  in  this  monograph.  I  have  answered  the  question  in 
the  affirmative  after  considerable  reflection  and  acted  accord- 
ingly, for  on  the  one  hand  the  limit  separating  works  worth 
quoting  from  others  not  worth  quoting  is  not  always  easy  to 
draw  and  might  be  decided  differently  according  to  the  person 
making  the  decision,  and  as  many  times  a  small  grain  of  gold 
may  be  hidden  under  much  rubbish,  and  yet  in  truth  serve  as  a 
crystallizing  point  for  further  investigations  and  also,  however. 


BY   ELECTROLYSIS   OF   AQUEOUS   SOLUTIONS.  II 

l>e  highly  detrimental  to  the  claims  of  later  investigators. 
Any  one  who  has  had  much  to  do  with  the  taking  out  of  pat- 
ents has  probably  had  the  experience  that  the  remarks  of 
many  patentees  are  so  general  that  they  frequently  cover  more 
particulars  than  was  intended,  and  their  generalities  frequently 
include  in  their  terms  facts  which  were  completely  unknown 
to  the  patentee,  but  such  generalities  are  frequently  of 
great  hindrance  and  burdensome  to  applicants  for  new  pat- 
ents ;  naturally  in  the  second  case  an  exact  knowledge  of 
the  literature  would  be  of  considerable  use. 

This  monograph  endeavors,  in  contrast  with  the  yearly  re- 
ports, etc.,  to  give  a  complete  compilation  of  the  subject  of 
such  extensiveness  as  shall  make  superfluous  the  necessity  of 
referring  to  the  frequently  difficultly  accessible  original  litera- 
ture. We  wish  first  to  find  our  bearings  in  the  mass  of  ma- 
terial to  be  found  in  this  field,  valuable  and  valueless.  On 
these  grounds  I  did  not  deem  a  selection  admissible. 

A  second  patent1  of  Placet  and  Bonnet  is  concerned  directly 
with  the  electrolytic  production  of  chromium.  The  inventors 
state  that  it  is  necessary  in  manufacturing  chromium  and 
chromium  alloys  electrolytically  to  keep  the  content  of  chro- 
mium in  the  bath  constant  during  the  whole  duration  of  the 
process.  The  electrical  conductivity  of  the  bath  is  increased 
by  adding  sulphates  or  chlorides  of  the  alkalies,  or  alkaline 
earths;  the  addition  of  organic  materials  like  gum  and  dex- 
trin is  also  useful. 

Regarding  the  concentration  of  the  chromium  salt  solution 
itself,  they  recommend  to  use  only  about  one-fifth  of  the  quan- 
tity of  salt  necessary  to  make  a  completely  saturated  solution; 
the  solution  is  preferably  to  be  warmed. 

The  nature  of  the  metallic  precipitate  is  favorably  in- 
fluenced by  making  the  surface  of  the  anode  larger  than  that 
of  the  cathode.  As  anodes,  soluble  and  insoluble  materials 
may  be  used,  but  it  is,  however,  always  to  be  recommended 
that  in  order  to  avoid  the  contamination  of  the  baths  and  the 

1  German  Patent  No.  66,099,  December  5,  1890. 


12  CHROMIUM  AND  ITS  COMPOUNDS. 

polarization  resulting  from  gas  bubbles,  diaphragms  should 
be  used  and  to  place  in  the  anode  compartment  such  fluids 
as  will  combine  with  the  oxygen  there  liberated  ;  for  instance 
sulphuric  acid,  hydrochloric  acid,  sodium  chloride  solution, 
sulphurous  acid,  etc. 

To  keep  the  chromium  content  of  the  bath  constant,  solid 
chromium  salt  is  to  be  added  from  time  to  time. 

A  tension  of  30  to  40  volts  (!)  is  recommended  as  particu- 
larly advantageous  for  operating  the  bath. 

If  alloys  are  to  be  directly  precipitated  the  salt  of  the  metal 
to  be  alloyed  is  dissolved  in  the  bath  just  described  or  the 
metal  to  be  alloyed  is  used  as  a  soluble  anode  in  a  one-half  or 
three-quarter  saturated  solution  of  the  alkalies  or  the  alkaline 
earths  and  the  current  used  at  that  tension  "  which  corresponds 
to  the  composition  of  the  alloy." 

For  example,  if  it  is  wished  to  alloy  iron  with  chromium  it 
is  well  to  add  about  one-quarter  of  the  quantity  of  iron  salt  to 
the  solution  that  would  be  necessary  to  saturate  it,  and  about 
one-fifth  of  that  quantity  of  chromium  salt  which  would  like- 
wise saturate  the  liquid  in  the  absence  of  any  other  salt.  To 
the  solution  thus  formed  is  added  as  much  alkali  or  alkaline 
earth  salt  as  it  will  take  up. 

"  The  alloy  can  either  be  directly  extracted  from  such  a 
bath  or  the  two  metals  may  be  deposited  consecutively,  but 
one  upon  the  other  and  subsequently  melted  together  to  the 
alloy."  In  both  cases  the  composition  of  the  alloy  may  be 
regulated,  "  in  the  first  case  by  using  a  certain  determined 
tension,  in  the  latter  by  the  duration  of  the  action  of  the 
current  on  the  bath.  At  6  volts  tension  only  iron  separates 
out,  at  30  volts  only  chromium."  By  using  intermediate  ten- 
sions, alloys  of  any  composition  desired  may  be  obtained. 
The  latter  can  also  be  obtained  by  precipitating  first  the  iron 
with  a  tension  of  6  volts,  then  the  chromium  at  a  tension  of 
30  and  finally  melting  the  precipitated  metals  together. 

Patent  Claim. 

The  electrolytic  obtaining   of   chromium    and    its   alloys, 


BY   ELECTROLYSIS   OF   AQUEOUS   SOLUTIONS.  13 

characterized  by  adding  to  the  solution  of  chromium  salt  in 
about  five  times  the  volume  of  water  necessary  to  dissolve  it, 
materials  which  will  not  chemically  injure  the  metal  to  be 
precipitated,  for  instance,  alkali  or  alkaline  earth  sulphates, 
chlorides,  or  similar  salts  alone  or  in  combination  with  or- 
ganic materials,  gum,  dextrin  or  similar  materials,  such  ma- 
terials being  added  to  saturation  and  the  mixture  electrolyzed 
hot  or  cold,  keeping  the  chromium  content  of  the  bath  as  con- 
stant as  possible. 

The  next  patent1  of  the  same  inventors  is  entitled :  "  Im- 
provements concerning  the  electrolysis  of  metals."  They 
refer  to  their  first  English  patent  No.  19,344  of  1890  (page  3) 
and  now  propose  to  avoid  the  formation  of  oxide  at  the  cathode 
by  the  use  of  acid  salts  (bisulphates  and  phosphates,  acetates, 
etc.)  in  place  of  acids.  It  is  particularly  difficult  to  find  the 
correct  amounts  of  acid  to  add  in  depositing  chromium  from 
the  solutions  containing  10-15  grams  of  chromium  alum,  10- 
15  grams  of  sodium,  potassium  or  ammonium  sulphates  or  a 
mixture  of  these  sulphates  in  100  grams  of  water,  whereas,  on 
the  other  hand,  they  obtain  at  once  a  particularly  fine  chro- 
mium deposit  by  using  bisulphates  in  place  of  the  sulphates, 
as  for  instance  10-15  grams  of  bisulphate  to  10-15  grams  of 
chromium  alum  in  100  grams  of  water.  In  case  the  bisul- 
phates contain  free  acid  the  corresponding  quantity  of  normal 
sulphate  is  to  be  mixed  with  it.  Besides  chromium,  chromium 
alloys  as  well  as  other  metals  may  be  precipitated  from  the 
corresponding  solutions. 

The  patent  claim  reads :  The  use  of  strong  polybasic  salts 
alone  or  mixed  with  neutral  salts  in  order  to  obtain  electro- 
lytic precipitates  of  chromium,  aluminium,  copper,  iron,  nickel, 
cobalt,  tungsten,  molybdenum,  antimony,  tin,  silver,  etc., 
and  their  alloys  in  the  above-described  way. 

In  two  further  patents  taken  out  at  the  same  time,  Placet 
and  Bonnet  protect  several  modifications  of  their  process  for 
making  chromium. 

1  English  Patent  22,854,  Dec.  31,  1891. 


14  CHROMIUM  AND  ITS  COMPOUNDS. 

The  first  patent1  bears  the  title:  "  A  method  for  the  precipi- 
tation of  chromium  with  the  assistance  of  electrolytic  baths 
containing  chromium  salts. 

The  bath  used  is  again  given  the  composition  of  10,  15,  to 
20  grams  of  chromium  sulphate  with  100  grams  of  water  to 
which  besides  is  added  so  much  sulphuric  acid  that  no  forma- 
tion of  oxide  can  take  place  at  the  negative  electrode.  In 
place  of  chromium  sulphate  may  also  be  used  chrome  alum, 
in  place  of  sulphuric  acid,  either  nitric,  hydrochloric  or  hydro- 
fluoric and  organic  acids  or  a  mixture  of  the  same.  First- 
class  precipitates  are  said  to  have  been  obtained  for  instance 
by  using  a  bath  of  10  to  15  grams  of  chrome  alum,  10  to  15 
grams  of  sodium  or  potassium  sulphate,  5  grams  oxalic  acid 
or  some  other  organic  acid  and  100  grams  of  water,  heated 
until  the  originally  green  solution  has  become  violet  and 
then  electrolyzed. 

The  solution  of  alkaline  chromate  or  bichromate  to  which 
some  sulphate  is  added  may  also  be  used,  and  for  the  accelera- 
tion of  the  reaction  the  addition  of  a  little  alcohol  is  recom- 
mended. The  chromium  salt  preferably  used  is  the  sulphate 
or  a  chrome  alum  in  about  the  following  proportions  :  10  to 

15  grams  of  chromate  or  bichromate  with    10  to  15  grams 
of  chrome  alum  and  100  grams  of  water. 

In  place  of  the  chromate  the  more  costly  chromic  acid  may 
be  used  and  in  place  of  the  chrome  alum  other  chromium 
salts  such  as  the  nitrate.  Alkaline  chromium  baths  likewise 
furnish  chromium  when  electrolyzed,  even  if  the  chromium 
solution  gives  a  precipitate  with  alkali  ;  the  same  is  true  of 
baths  containing  cyanides  or  sulphocyanides  of  the  alkalies, 
and  finally  chromium  may  be  electrolytically  precipitated 
from  solutions  of  the  roseo-chrome  salts  or  ammoniacal 
chrome  compounds. 

For  raising  the  conductivity  there  may  be  added  to  any  of 
these  baths  10  to  15  per  cent,  of  alkali  sulphate  or  ammonium 
sulphate  or  a  mixture  of  both  or  alkali  nitrates,  phosphates, 

1  English  Patent  22,855,  Dec.  31.  1891.     U.  S.  Patent  526,114. 


BY   ELECTROLYSIS   OF   AQUEOUS   SOLUTIONS.  15 

etc.,  so  that  the  bath  may  consist  of,  foi  instance,  10  to  15 
grams  of  chrome  alum  or  chromium  fluoride,  10  to  15 
grams  of  sodium,  potassium  or  ammonium  fluorides,  5  to 
10  grams  of  hydrofluoric  acid  or  another  acid. 

In  case  a  heavy  precipitate  is  desired  in  a  short  time  the 
bath  must  be  heated  to  higher  temperatures.  "  In  many  cases 
we  heat  our  baths  so  high  that  the  salts  are  melted  v  (see  later). 

The  composition  of  the  solution  is  kept  constant  either  by 
using  soluble  anodes  or  by  circulation.  The  addition  of  small 
quantities  of  alcohol,  sugar,  glycerin  or  analogous  organic 
compounds  exercise  a  favorable  influence  upon  the  qualities 
of  the  precipitated  metal. 

Finally,  alloys  can  be  made  by  using  the  baths  described 
and  adding  the  salt  of  the  other  metal.  An  alloy  may  also  be 
obtained  by  the  alternate  precipitation  of  chromium  and  the 
other  metal  and  subsequent  melting  down. 

The  patent  claim  reads :  The  use  of  an  electrolytic  bath 
containing  chromium  salts  in  the  manner  and  for  the  purpose 
described. 

The  second  patent1  has  the  title :  A  method  for  the  pre- 
cipitating of  chromium  by  the  use  of  electrolytic  baths  con- 
taining chromic  acid  salts.  The  baths  described  therein  need 
to  contain  only  i  to  2  grams  of  chromic  acid  in  100  grams  of 
water  ;  however,  with  increasing  concentration  the  quantity  of 
deposit  increases.  The  shade  of  the  precipitated  metal  alters 
if  small  quantities — 5  to  10  grams  per  litre — of  the  following 
acids  are  added :  Phosphoric,  sulphuric,  oxalic,  benzoic,  formic, 
gallic,  pyrogallic,  picric,  purpuric  (?)  (phenic),  salicylic  ;  all 
such  solutions  give  white  chromium  deposits. 

Acetic  and  hydrofluosilicic  acids  give  shining  but  dark  de- 
posits, boric  acid  dead  but  very  copious  deposits,  while  by  adding 
sulphuric,  nitric,  hydrochloric,  arsenic,  tartaric,  citric,  lactic 
or  tannic  acids  the  metal  is  more  or  less  dark  according  to  the 
quantity  added.  It  may  be  noticed  also  that  the  chromic  acid 
necessary  for  the  baths  may  be  manufactured  by  the  electro- 

1  English  Patent  22,856,  Dec.  31,  1901. 


1 6  CHROMIUM  AND  ITS  COMPOUNDS. 

lytic  oxidation  of  chromic  salts  ;  also  that  alloys  of  chromium 
and  other  metals  may  be  obtained  from  solutions  containing 
chromic  acid  and  other  metals. 

The  claim  reads :  The  use  of  electrolytic  baths  containing 
chromic  acid  in  the  manner  and  for  the  purpose  described. 

In  an  article1  published  in  1892,  "The  Manufacture  of 
Metallic  Chromium  by  Electrolysis,"  E.  Placet  presents  nothing 
new.  He  only  repeats  that  a  beautiful  lustrous  deposit  of 
pure  chromium  was  obtained  by  electrolyzing  an  aqueous  so- 
lution of  chrome  alum  to  which  alkaline  sulphates  and  a 
small  quantity  of  sulphuric  or  other  acid  has  been  added. 
Also  chromium  coatings  on  bronze,  brass,  copper  and  even 
iron  of  any  desired  thickness  and  resembling  oxidized  silver 
can  be  obtained  in  this  manner.  There  was  shown  at  a 
meeting  of  the  Academy,  when  this  article  was  read,  a  piece  of 
metallic  chromium  weighing  more  than  a  kilogram,  chro- 
mium alloys  and  brass  accoutrements  electrolytically  coated 
with  chromium. 

In  reference  to  the  qualities  of  the  metal  so  obtained,  which 
was  then  being  industrially  produced,  it  was  mentioned  that 
it  was  of  a  bluish  white  color,  very  hard  and  extraordinarily 
resistant  alike  to  atmospheric  influences  as  also  to  concentrated 
sulphuric  acid,  nitric  acid  and  caustic  potash  solution. 

If  the  baths  are  electrolyzed  under  certain  conditions,  groups 
of  chromium  crystals  are  obtained  which  have  the  form  of 
pine  tree  branches. 

The  fruitfulness  of  the  two  inventors  E.  Placet  and  J.  Bon- 
net is  not  exhausted  by  the  five  patents  already  described  ; 
two  years  later  we  run  across  a  new  patent2  worded  thus  "  Im- 
provements in  the  electrolytic  manufacture  of  chromium  and 
chromium  alloys." 

They  commence  with  one  of  the  observations  made  in  a 
former  patent  (see  page  15)  according  to  which  they  heat  the 
baths  in  some  cases  so  high  that  the  salts  are  melted,  and  give 
us  the  following  additional  information  thereon : 

1  Comptes  rendus,  115,  945  (1892). 

2  English  Patent  6,751,  March  30,  1893. 


BY   ELECTROLYSIS   OF   AQUEOUS   SOLUTIONS.  1 7 

We  take,  they  say,  for  instance  10  to  15  grams  of  potassium 
bisulphate,  100  grams  of  chrome  alum  and  100  grams  of  water, 
bring  the  salts  into  solution  by  heating  and  electrolyze ; 
chromium  precipitates  at  once  upon  the  cathode.  The  con- 
centration of  the  bath  is  kept  up  by  the  addition  of  chromium 
alum  or  a  concentrated  solution  of  chromium  alum  and  alkali 
bisulphate  ;  by  doing  this  the  volume  increases  and  on  this  ac- 
count an  overflow  is  provided  to  keep  the  level  of  the  bath 
constant.  In  case  only  chromium  alum  is  added  all  the  water 
originally  in  the  solution  is  soon  used  up  and  the  bath  con- 
sists only  of  the  salts  "  reduced  either  by  water  or  by  heat(?)." 

According  to  that,  water  can  be  dispensed  with  for  the  for- 
mation of  the  bath  and  the  latter  be  formed  by  directly  melt- 
ing down  the  mixture  of  salts.  If  that  is  so  when  and  where 
could  we  add  to  the  bath  a  little  potassium  chlorate,  boric 
acid,  benzoic  acid  or  analogous  material(!)  in  order  to  facilitate 
the  precipitation  of  the  metal.  In  place  of  the  potassium  bi- 
sulphate there  may  be  used  as  a  flux  either  sodium  or  am- 
monium sulphate  or  bisulphates  or  the  phosphates,  borates, 
chlorates,  silicates,  chlorides,  fluorides,  etc.,  of  the  alkalies  or 
alkaline  earths  or  mixtures  of  the  same ;  in  place  of  the 
chrome  alum  also  chromic  oxide  and  all  other  chromium 
salts  which  melt  easily  when  mixed  with  the  alkaline  earths. 
On  account  of  the  high  melting-point  of  chromium  we  usually 
use  an  electric  furnace  and  in  place  of  pure  carbon  electrodes 
we  use  electrodes  made  of  a  mixture  of  carbon,  chromic  oxide, 
chromic  salts  or  ores,  a  flux  as  borax,  etc.,  and  a  reducing 
agent  (like  zinc,  magnesium,  aluminium,  etc.)  so  that  the 
metal  is  simultaneously  reduced  and  melted. 

If  chromium  alloys  are  to  be  immediately  produced  the 
electrodes  may  be  made  of  the  alloying  metal  (copper, 
aluminium,  silver,  nickel,  zinc)  or  of  their  oxides. 

It  is  finally  recommended  to  introduce  into  the  melting 
crucible  indifferent  or  reducing  gases,  as  hydrogen,  etc.,  and 
as  the  simplest  manner  of  introduction  through  hollow  elec- 
trodes. 


1 8  CHROMIUM  AND  ITS  COMPOUNDS. 

The  patent  claim  reads  :  i.  The  above-described  improve- 
ments in  the  obtaining  of  metallic  deposits  of  chromium  of 
any  thickness  and  in  considerable  quantities  for  commercial 
purposes.  2.  The  above-described  improvements  in  chro- 
mium coating  various  articles,  among  others  of  carbon  fila- 
ments and  rods  such  as  are  used  in  electric  lighting.  3.  The 
above-described  improvements  for  the  direct  electrolytic  pro- 
duction of  alloys  of  chromium  and  other  metals. 

My  opinion  of  the  contents  of  this  patent  of  Placet  and 
Bonnet  is  a  repetition  of  what  I  have  said  on  page  10.  In  order 
to  give  my  judgment  some  experimental  justification  I  have 
had  Mr.  Shick  produce  and  electrolyze  in  my  laboratory  some 
of  the  baths  recommended  in  the  patent  specifications. 

I  quote  some  extracts  from  the  report  of  Mr.  Shick  : 

A  well-saturated  solution  of  chromic  sulphate  at  the  tem- 
perature of  the  room,  was  used  and  100  cc.  diluted  to  600  cc. 
with  water  and  then  sodium  chloride  added  to  saturation.  A 
platinum  foil  was  used  in  each  case  as  cathode.  With  40 
sq.  cm.  active  cathode  surface,  using  a  current  density  of 
0.2  ampere  per  sq.  cm.  there  was  obtained  a  quite  small 
black  precipitate  which  from  its  behavior  appeared  to  be  chro- 
mium. With  a  current  density  of  0.3  ampere  per  sq.  cm. 
no  precipitate  was  obtained.  A  precipitate  .did  not  appear 
also  when  the  above  bath  was  saturated  with  sodium  sulphate 
instead  of  sodium  chloride  and  electrolyzed  at  30°  and  80° 
with  a  current  of  0.2  and  0.3  ampere  per  sq.  cm. 

Another  bath  was  prepared  with  15  grains  of  chromium 
alum  and  15  grams  of  potassium  bisulphate  dissolved  in  100 
grams  of  water. 

Also  in  this  case  there  was  obtained  with  the  above  current 
densities  and  varying  temperatures  only  at  the  most  traces  of 
chromium  deposits. 

Other  baths  gave  no  better  results.  It  is  sufficient  therefore 
to  merely  mention  the  baths  used  and  to  notice  that  in  all 
cases  good  circulation  was  obtained  by  active  motion  of  the 
cathode. 


BY   ELECTROLYSIS   OF   AQUEOUS   SOLUTIONS.  19 

Bath  III. — Fifteen  grams  of  chrome  alum,  15  grams  of  am- 
monium fluoride,  10  grams  of  concentrated  hydrochloric  acid 
and  100  grams  of  water. 

Bath  IV. — Fifteen  grams  of  chrome  alum.,  15  grams  of  bi- 
sulphate,  100  grams  of  water. 

These  statements  agree  entirely  with  the  results  of  other 
investigators  who  likewise  could  obtain  no  chromium  deposits 
in  the  manner  described.1  According  to  that  there  is  no  longer 
any  doubt  that  the  kilogram  of  chromium  (page  16)  exhib- 
ited at  the  French  Academy  by  Placet  could  not  have  been 
obtained  in  the  manner  stated  or  that  at  least  conditions  of 
the  highest  importance  for  the  obtaining  of  good  chromium 
deposits  were  not  then  stated  by  him. 

While  the  processes  so  far  described  attempt  to  obtain  me- 
tallic chromium,  and  the  accessory  phenomena  of  the  process 
were  only  very  slightly  or  not  at  all  noticed,  the  patent  of  the 
Electro-Metallurgical  Company,  Limited,2  about  to  be  de- 
scribed, lays  particular  weight  upon  these  phenomena.  The 
patentees  start  from  the  undotibtably  correct  point  of  view 
that  whoever  wishes  to  reach  an  economical  operation  must 
keep  in  view  two  other  points  besides  the  consumption  of 
electrical  energy,  points  which  have  an  important  influence 
upon  the  cost  of  the  metal ;  namely,  the  anodes  to  be  used 
and  the  nature  and  the  quantity  of  the  products  resulting. 
Since  platinum  electrodes  are  much  too  expensive  to  be  used  for 
the  production  of  chromium  it  is  preferable  to  use  chromium 
sulphate  solutions  for  the  electrolysis,  which  permits  of  the  use 
of  lead  anodes.  The  latter  are  coated  over  with  a  layer  of 
peroxide  which  protects  them  for  a  long  time  from  destruc- 
tion, provided  that  the  sulphuric  acid  is  no  more  concentrated 
than  is  usually  employed  in  lead  accumulators.  Care  must 
be  taken  on  this  point,  if  a  diaphragm  is  used  and  sulphuric 

1  Cowper-Coles  :  Chemical  News,  81,  16  (1900)  ;   J.  Fe"re*e  :  Bull.  Soc. 
Chim.,  [3]  231,  617  (1901). 

2  German  Patent  105,847,  Sept.   7,    1898.      The  corresponding  English 
Patent  No.  18,743,  f°r  1898,  is  under  the  name  of  Moller  and  Street. 


2O  CHROMIUM  AND  ITS  COMPOUNDS. 

acid  is  the  anode  fluid,  to  bear  in  mind  that  the  latter  becomes 
more  concentrated  during  electrolysis  and  must  therefore  be 
diluted  in  a  suitable  manner.  If  no  diaphragms  are  used  the 
content  in  sulphuric  acid  must  in  that  case  be  kept  low  in 
order  to  get  a  precipitate  of  chromium  at  all,  and  therefore 
there  is  no  need  of  giving  precautions  for  the  preservation  of 
the  electrode. 

The  second  object,  the  obtaining  of  by-products  which 
will  have  a  certain  marketable  value  and  at  the  same  time  to 
keep  their  quantities  down  to  the  minimum — is  obtained  by 
the  patentees  in  the  following  somewhat  complicated  manner. 

Imagine,  for  instance,  an  electrolytic  apparatus  provided 
with  a  diaphragm,  the  anode  solution  consisting  of  water 
acidulated  with  5  per  cent,  of  its  weight  of  concentrated  sul- 
phuric acid  of  66°  B.,  while  the  cathode  fluid  contains  to 
each  1.5  kilograms  of  water,  1.5  kilograms  of  sodium-chrome 
alum  and  1.5  kilograms  of  sodium  sulphate.  If  this  is  heated  to 
about  90°  and  electroly zed  with  a  current  density  of  0.4  ampere 
per  sq.  cm.  there  is  obtained  40  grams  of  chromium  per  ampere 
hour.1  As  the  electrolysis  proceeds  the  sulphuric  acid  in  the 
anode  compartment  becomes  more  concentrated,  as  already  de- 
scribed, and  also  sodium  sulphate  and  chromic  sulphate  pass  into 
it,  the  latter  being  oxidized  at  the  anode  to  chromic  acid.  An 
analysis  showed  that  during  the  obtaining  of  23.5  kilograms 
of  metallic  chromium  0.562  kilogram  of  chromic  acid  and 
0.936  kilogram  of  sodium  sulphate  passed  into  the  anode 
compartment. 

Since,  as  may  be  seen  from  the  formula  of  chromic  sulphate, 
294  grams  of  sulphuric  acid  are  set  free  at  the  electrode  for  104 
grams  of  chromium  precipitated,  a  works  which  manufactures 
a  ton  of  chromium  in  twenty-four  hours  would  obtain  nearly 
three  tons  of  sulphuric  acid  of  66°  B.,  but  in  a  diluted  condi- 
tion and  mixed  with  the  other  by-products  mentioned  and 
therefore  in  a  form  of  little  commercial  value.  In  order  to 

1  Apparently  this  is  a  mistake ;  in  the  English  patent  it  is  given  as  0.2 
gram,  which  Jwould  be  about  30  per  cent,  of  the  theoretical  amount. 


BY   ELECTROLYSIS   OF   AQUEOUS   SOLUTIONS.  21 

|| 

avoid  this  and  other  difficulties  the  process  was  operated  as 
follows : 

The  anode  liquid  after  it  has  become  somewhat  rich  in 
chromic  acid,  etc.,  is  treated  with  gaseous  sulphur  dioxide 
whereby  the  chromic  acid  is  reduced  to  chromic  sulphate  ; 
the  fluid  is  then  concentrated  to  30°  B.,  by  doing  which  the 
excess  of  sulphur  dioxide  is  driven  off.  Then  sodium  bi- 
chromate is  added  in  such  quantities  that  independently  of  the 
sodium  sulphate  formed  2CrO3  is  present  for  every  two  equiva- 
lents of  sulphuric  acid,1  and  allows  this  mixture  to  flow  in  a 
more  or  less  thin  stream  into  a  lead  vessel  which  contains 
always  an  excess  of  melted  sulphur  kept  at  130°.  The 
chromic  acid  oxidizes  the  sulphur,  and  chromic  sulphate  is 
formed  by  the  two  equivalents  of  free  sulphuric  acid  alluded 
to.  This  with  the  sodium  sulphate  formed  regenerates  the 
alum.  By  treating  with  some  water  and  filtering  from  the 
excess  of  sulphur  there  is  obtained  a  solution  of  chromic 
alum  (and  sodium  sulphate),  which  can  be  led  into  the  elec. 
trolyzing  apparatus  if  necessary. 

The  first  treatment  with  sulphurous  acid  can  be  omitted 
by  taking  account  of  the  chromic  acid  present  when  adding 
the  bichromate. 

Considering  the  reactions  in  the  cathode  compartment  there 
is  naturally  a  much  greater  depletion  of  the  chromic  sulphate, 
while  the  content  of  sodium  sulphate  is  only  slightly  altered. 
It  is  clear  that  under  such  conditions  with  a  cathode  solution 
saturated  with  sodium  chrome  alum  the  quantity  of  sodium 
sulphate  soon  reaches  such  a  point  that  the  operation  of  the 
apparatus  is  interrupted. 

This  interruption  in  fact  occurs  very  easily  as  was  empha- 
sized since  the  content  of  free  acid  in  the  solution  is  carefully 
regulated  in  order  to  obtain  a  good  output  and  the  quantity  of 

1  The  explanation  is  not  very  clear  ;  the  following  formula  according  to 
which  the  oxidation  apparently  proceeds  gives  the  relations  between  the 
chromic  acid  and  the  sulphuric  acid  : 

Na2Cr207  +  3H2SO4  +  S  -=  Cr.2(SO4)3  -f  Na2SO4  +  sH2O. 


22  CHROMIUM  AND  ITS  COMPOUNDS. 

p 

sodium  chrome  alum  and  the  accessory  salts  (in  the  foregoing 
case  sodium  sulphate)  must  stand  to  each  other  in  the  right 
proportions.  If  this  is  not  the  case,  the  following  occurrences 
take  place  : 

No  precipitate  of  chromium  comes  down,  the  bath  is  too 
acid. 

It  is  then  electrolyzed  some  time,  whereby  the  content  in 
acid  diminishes  of  itself  or  it  is  neutralized  by  means  of  chro- 
mium hydroxide  or  any  other  base  or  a  carbonate. 

There  results  chromic  acid  at  the  cathode,  a  sign  that  the 
addition  of  acid  is  necessary. 

There  occurs  also  the  necessity  of  removing  the  sodium 
sulphate  in  excess,  which  may  be  most  simply  done  by  cooling 
the  hot  cathode  liquor  and  crystallizing  out  the  sodium  sul- 
phate. 

It  may  be  seen  that  continuous  working  with  a  utilization 
of  the  by-products  may  be  achieved  in  this  way.  If  wished, 
other  changes  may  be  introduced.  Instead  of  supplying  the 
apparatus  with  chromium  alum,  chromic  sulphate  may  be  used 
in  which  case  the  sodium  sulphate  is  superfluous.  Further, 
the  acid  produced  in  the  anode  compartment  can  be  neutral- 
ized by  chromic  hydroxide  and  later  the  whole  anode  fluid,  if 
a  sufficient  migration  of  chromium  has  taken  place,  be  brought 
over  to  the  cathode  side.  In  that  case  it  is  previously  neces- 
sary to  reduce  the  chromic  acid  formed  by  sulphurous  acid 
and  neutralize  further  with  chromic  hydroxide.  Or  the  whole 
of  the  chromic  hydroxide  added  may  be  supplied  after  the  re- 
duction of  the  chromic  acid. 

Finally  it  is  remarked  that  the  process  may  also  be  carried 
out  without  diaphragms,  but  with  more  difficulty,  and  that  al- 
kali, earth  alkali  or  chromic  sulphides  are  proposed  for  the 
reduction  of  the  chromic  acid. 

The  patent  claims  read  : 

i.  Processes  for  the  obtaining  of  chromium  by  electrolysis 
of  salts  containing  chromic  sulphate,  using  lead  anodes,  and 
characterized  by  the  reduction  of  the  fluid  leaving  the  anode 


R  /* 
OF  THt 

UNIVERSITY 

BY   ELECTROLYSIS   OF   AQUEOUS   SOLUTIONS.  23 

compartment  by  sulphurous  acid  and  further  treatment  with 
melted  sulphur,  whereby  chrome  alum  is  formed  when  sodium 
chromate  is  added,  and  the  chrome  alum  being  then  conducted 
to  the  cathode  compartment,  the  cathode  fluid  being  circulated 
and  its  temperature  kept  low  in  order  to  avoid  its  enrichment 
in  sodium  sulphate. 

2.  A  method  of  carrying  out  the  process  of  Claim  i,  char- 
acterized by  saturating  the  fluid  coming  from  the  anode  com- 
partment, after  its  reduction  by  sulphurous  acid, with  chromium 
hydroxide,  and  thereupon  using  it  for  supplying  the  cathode 
compartment. 

After  working  one's  way  through  this  patent  specification 
one  has  not  the  feeling  that  it  is  a  process  proved  through 
practical  investigations,  and  which  has  been  found  profitable. 

At  this  place  we  may  also  mention  the  process  of  the  same 
company — Electro-Metallurgical  Company — intended  to  ren- 
der possible  exact  control  of  electrolytic  metal  depositions  and 
especially  chromium  deposition.1  The  company  has  found  out 
in  their  investigations  (see  also  Bunsen,  page  i)  that  using 
a  chromium  bath  with  sulphate  salts  of  known  composition 
and  keeping  the  current  strength  constant  the  alteration  of 
the  amount  of  cathode  surface  changes  the  nature  of  the  pre- 
cipitate. "  There  is  obtained,  for  instance,  from  the  same  bath 
and  with  the  same  current  strength  a  precipitate  of  oxide  if  a 
rod  8  mm.  diameter  is  used,  but  with  a  rod  of  15  mm.  diame- 
ter a  fine  metallic  precipitate  which  increases  in  thickness 
with  a  good  efficiency  of  deposition.  With  a  rod  18  mm.  in 
diameter  a  precipitate  is  obtained  which  does  not  increase  in 
thickness,  and  finally  with  a  rod  of  20  mm.  in  diameter  no 
precipitate  is  obtained.  These  figures  are  only  given  by  way 
of  example  ;  according  to  the  composition  of  the  bath  and  its 
content  of  free  acid,  they  are  quite  different." 

For  a  given  bath  which  with  a  certain  current  strength 
gives  a  good  precipitate  on  a  rod  15  mm.  thick,  there  may  be, 
therefore,  easily  found  the  diameter  of  a  rod  which  will  give 

1  German  Patent  No.  104,793,  Sept.  7,  1898. 


24  CHROMIUM  AND  ITS  COMPOUNDS. 

in  the  same  bath  a  chromium  precipitate  which  does  not  in- 
crease in  thickness.  As  long  as  the  composition  of  the  solu- 
tion suffers  no  material  change,  the  chromium  precipitate  upon 
the  first  rod  will  increase  in  thickness  as  is  desired,  while  the 
weight  of  the  second  rod  remains  unchanged.  The  reverse  is 
true,  that  an  alteration  in  the  weight  of  the  test  rod  would  be 
a  sign  that  the  solution  had  changed,  and  that  a  chromium 
precipitate  upon  the  first  rod  was  not  coming  down  in  the 
properly  prescribed  manner. 

In  order  then  that  the  test  rod  which  should  remain  of  con- 
stant weight  may  act  as  an  automatic  signal  of  the  current  it 
is  hung  from  the  arm  of  a  balance  whose  other  arm  is  fur- 
nished with  contacts  which  ring  an  electric  bell  as  soon  as  the 
test  rod  loses  or  gains  in  weight.  To  make  the  bell  stop  ring- 
ing and  bring  the  electrolyte  again  into  proper  condition  the 
bath  must  be  neutralized  if  the  weight  of  the  rod  has  decreased, 
or  acidified  if  it  has  increased. 

"  The  process  permits  of  finding  out  with  exactness  the 
condition  of  the  electrolyte  and  thereby  regulating  properly 
the  operation  of  the  apparatus." 

The  patent  claim  reads  : 

A  process  for  the  control  of  electrolytic  depositions  of  metals 
characterized  by  the  use  of  a  test  rod  which  is  connected  in 
parallel  in  the  precipitating  bath,  the  dimensions  of  the  rod 
being  so  chosen  that  with  a  proper  current  density  and  with 
normal  content  of  acid  the  test  rod  is  covered  with  only  a 
light  deposit  as  may  be  determined  by  removing  it  from  the 
bath  or  by  hanging  it  from  the  arm  of  a  balance.  In  the 
latter  case  the  other  arm  of  the  balance  should  be  connected 
with  an  electric  bell  whereby  the  increase  of  acid  content  of 
the  bath  or  the  diminution  of  metal  in  the  bath  on  the  one 
hand,  or  the  decrease  of  the  content  in  acid  or  the  increase  of 
metal  precipitated  on  the  test  rod  on  the  other  hand,  causes  a 
movement  of  the  arm  of  the  balance  and  the  closing  of  the 
circuit  through  the  electric  bell. 

The  series  of  patents  concerning  the  electrolytic  precipita- 


BY    ELECTROLYSIS   OF  AQUEOUS   SOLUTIONS.  25 

tion  of  chromium  from  aqueous  solutions  is  herewith  ex- 
hausted. We  have  to  add  to  them  simply  two  scientific 
articles  on  this  subject. 

J.  Feree1  states  that  he  has  obtained  steel-gray  chromium 
99.82  per  cent,  pure  by  using  a  platinum  cathode  and  electro- 
lyzing  a  solution  of  740  grams  of  water,  100  grams  of  hydro- 
chloric acid  and  160  grams  of  crystallized  chromic  chloride 
(see  also  under  chromium  amalgam.)  The  current  density 
used  is  0.15  ampere  per  sq.  cm.,  tension  8  volts. 

He  obtained  a  silver-white  precipitate  of  finer  appearance 
from  a  solution  of  chromium-potassium  chloride;  266.5 
grams  CrCl3  -f  6H2O  (i  molecule)  and  223.5  grams  KC1 
(3  molecules)  were  dissolved  in  one  litre  of  water  and  the  cur- 
rent density  and  tension  used  were  as  above.  With  15  sq. 
cm.  cathode  surface  the  weight  of  the  precipitate  was  3  grams 
corresponding  to  an  ampere-efficiency  of  45  per  cent. 

The  author  complains  that  often  processes  for  the  electro- 
lytic precipitation  of  chromium  are  described  without  exact 
data  being  given  (compare  the  foregoing  chapter),  and  states 
that  he  has  tried  in  vain  to  get  chromium  from  a  solution  of 
chromium  sulphate  acidulated  with  sulphuric  acid  and  satu- 
rated with  alkaline  sulphates, — as  Placet  claimed  to  have  done 
(see  page  18). 

The  electrolytically  obtained  metal  is  very  hard  and  un- 
changeable at  ordinary  temperature.  At  a  red  heat,  it  covers 
itself  with  a  light  layer  of  green  chromic  oxide. 

It  is  unattacked  by  either  concentrated  sulphuric  or  nitric 
acid,  and  is  not  acted  upon  by  a  concentrated  solution  of 
caustic  potash. 

Some  further  data  on  electrolytically-precipitated  chromium 
has  been  given  by  Co wper- Coles.2  According  to  this  writer, 
chromium  precipitated  upon  copper  can  be  scratched  by  the 
diamond  point  only  when  it  is  weighted  with  0.07  gram. 
Electroplated  nickel  requires,  for  instance,  o.oi  gram,  elec- 

1  Bull.  Soc.  Chim.  [3],  25,  617  (1901). 
*  Chem.  News,  81,  16  (1900). 


26  CHROMIUM  AND  ITS  COMPOUNDS. 

troplated  palladium  0.066  gram,  a  brilliant  palladium  precip- 
itate 0.09  gram.  Fused  chromium  is  still  harder. 

The  capability  of  reflecting  light  is  soon  diminished  in  the 
case  of  chromium  by  tarnish,  which  accumulates  under  the 
same  conditions  much  stronger  than  with  silver,  platinum  or 
palladium.  In  the  finely  polished  condition  its  capability  of 
reflection  is  equal  to  that  of  silver. 

When  making  this  communication  Cowper-Coles  stated 
that  he  had  made  experiments  on  the  production  of  chromium 
alloys  electrolytically  and  had  taken  out  a  patent  for  the  same 
in  March,  1884,  but  I  have  not  been  able  to  discover  the  same. 
He  manufactured  chromium  alloys  by  heating  chromium  com- 
pounds with  charcoal  in  a  closed  crucible  and  pouring  upon 
the  reduced  mass  2  J^  parts  of  copper  and  then  i  to  i  J^  parts 
of  melted  tin  ;  the  whole  was  then  granulated,  again  melted 
and  cast  into  the  desired  form.  "  The  plates  thus  formed  were 
used  as  anodes  in  a  solution  which  is  made  by  dissolving  i 
pound  of  potassium  cyanide  and  i  pound  of  ammonium  car- 
bonate in  a  gallon  of  water  at  53  °C.  until  a  good  precipitate 
was  obtained  on  the  cathode,  using  a  low  current  density."  It 
must  be  granted  that  these  data  are  somewhat  hazy. 

Later  he  reports  on  several  new  investigations.  He  ob- 
tained a  fine,  lustrous  precipitate  of  chromium  from  a  solution 
of  25  parts  of  chromic  chloride  in  75  parts  of  water  electro- 
lyzed  at  75 °C.,  with  a  current  density  of  40  to  50  amperes 
per  square  foot  (0.3  ampere  per  square  meter).  No  metal  is 
obtained  from  a  cold  solution,  but  only  a  black  non-adhering 
precipitate  ;  the  tension  was  4  volts.  An  evolution  of  gas  took 
place  at  both  electrodes.  Good  precipitates  could  be  obtained 
only  by  the  use  of  an  excess  of  hydrochloric  acid,  which 
dissolving  the  precipitate  of  chromic  oxide  kept  the  bath  clear; 
according  to  this  the  chromium  chloride  solution  before  men- 
tioned would  have  to  be  acid. 

Chromium  could  not  be  obtained  either  in  the  cold  or  warm 
solution  containing  100  parts  of  water  to  100  parts  of  chrome 
alum  and  12  parts  of  barium  sulphate  (potassium  sulphate), 


BY   ELECTROLYSIS   OF   AQUEOUS   SOLUTIONS. 


using  current  densities  between  15  and  90  amperes  per  square 
foot.  The  anodes  used  were  carbon  and  platinum,  and  the 
cathode  copper.  The  tension  was  about  4  volts. 

Finally,  we  mention  a  work  of  B.  Neumann1  appearing  in 
1901,  in  which  the  different  conditions  were  determined  which 
are  of  importance  for  separating  out  chromium.  His  investi- 
gation was  very  properly  based  upon  determining  singly  the 
influences  of  current  strength,  density,  concentration  and  tem- 
perature with  different  solutions.  His  data  are,  on  this  ac- 
count, of  importance  and  we  will  consider  them  in  detail. 

The  experiments  were  carried  out  by  G.  Glaser  with  the 
use  of  diaphragms ;  the  cathode  space  contained  the  chromium 
solution,  and  the  anode  space  mineral  acid  or  salt  solution. 
The  cathode  was  ordinary  carbon,  but  the  metal  deposited 
adheres  also  to  metals  such  as  platinum,  brass  or  lead ;  the 
anode  was,  according  to  the  solution,  lead,  platinum,  or  car- 
bon. A  strong  circulation  of  the  cathode  fluid  is  important 
for  the  obtaining  of  useful  deposits  because  otherwise  the 
solution  at  the  cathode  becomes  too  much  impoverished  when 
using  high  current  densities  and  in  that  case  no  metal,  but 
only  chromous-chromic  oxide  is  precipitated. 


Current  den- 
sity in  amperes 
per  square 
centimetre. 

Product  separated  out. 

Ampere 
output  in 
percentage. 

0.009 
O.OlS 
0.036 
0.045 

0.072 

0.091 
0.137 
0.182 

At  first  metal  then  chromous-chromic  oxide  .... 
Metal  mixed  with  chromous-chromic  oxide  
Thin  layer  of  metal  upon  which  later  is  depos- 

5-4 

23-4 

38-4 
38.0 
38.6 

Metal  with  a  small  amount  of  chromous-chromic 

These  results  were  obtained  with  a  chromic  chloride  solu- 

1  Zeitschr.   f.  Blektrochemie,  7,    656  (1901).     A  lecture   given  at  the 
general  meeting  of  the  German  Electrochemical  Society  at  Freiburg,  Baden. 


28 


CHROMIUM  AND  ITS  COMPOUNDS. 


tion  containing  100  grams  of  metallic  chromium  per  litre, 
electrolyzed  at  the  temperature  of  the  room. 

If  the  temperature  is  varied  while  the  current  density  re- 
mains constant  it  is  found  that  the  precipitate  remains  good 
up  to  about  50°  but  over  50°  the  chromium  deposits  as  a 
black  powder ;  the  output  changes  very  little. 

The  alteration  of  the  concentration  of  the  solution  gave  the 
following  results : 


Concentration 
in  grams  of 
chromium  per 
litre  of  solu- 
tion. 

The  product  separated  out. 

Ampere 
output  in 
percentage. 

210 
184 
158 
135 
105 
79 
53 
26 

Metallic  powder  mixed  with  chromous  chloride-  •  • 
Metallic  powder  mixed  with  chromous  chloride-  .  - 

56.6 
49.0 
38.4 

At  first  metal,  then  chromous-chromic  oxide  

A  trace  of  chromous-chromic  oxide  and  a  strong 

The  current  density  at  which  these  tests  were  made  is  not 
particularly  given;  probably  it  lay  between  0.09  and  0.18 
ampere  per  square  centimetre. 

There  follows  the  incomprehensible  remark  that  the  ampere 
output  was  increased  from  51  per  cent,  up  to  89.5  per  cent, 
by  changing  the  anode  solution.  Or  should  this  read  "by 
changing  the  cathode  solution?" 

All  the  preceding  measurements  were  made  on  chromic 
chloride  solutions ;  sulphate  and  acetate  solutions  gave  simi- 
lar results  except  that  the  values  for  the  separation  of  metal 
in  the  concentration  and  current  density  tables  are  changed. 
The  best  proportion  for  sulphuric  acid  solutions  with  65  to 
85  grams  of  chromium  to  a  liter  was  at  0.13  to  0.20  ampere 
per  square  centimetre  current  density,  using  which  the  current 
output  of  84.6  per  cent,  was  reached.  The  influence  of  tem- 
perature was,  as  with  the  chloride,  of  slight  importance  ;  in 


BY   ELECTROLYSIS   OF   AQUEOUS   SOLUTIONS.  29 

the  most  favorable  cases  the  current  output  rose  to  86.2  per 
cent. 

The  acetate  solutions  gave  imperfect  precipitates  and  very 
deficient  current  output. 

Concerning  the  properties  of  the  electrolytically  precipita- 
ted chromium  it  was  said  that  it  showed  the  tendency  like 
nickel  to  spring  off  in  thin  sheets.  In  spite  of  that,  white  de- 
posits were  made  on  the  cathode  several  mm.  in  thickness.  If 
the  cathode  itself  is  rapidly  rotated  branch-like  deposits  several 
millimeters  in  length  with  crystalline  projections  are  formed. 
On  breaking  thick  pieces,  a  laminated  structure  is  plainly  to 
be  seen,  which  in  fact  comes  from  thin  formations  of  chromous- 
chromic  oxide  lying  between  the  laminae.  The  metal  is  bright 
gray,  frosted,  and  resembles  white  steel.  In  thin  layers  it  is 
silvery.  Its  purity  is  high,  containing  only  o.i  to  0.2  per 
cent,  of  iron,  while  commercial  chromium  usually  has  a  purity 
of  only  97  to  98  per  cent,  on  an  average,  though  purer  kinds 
may  be  produced.  Electrolytic  chromium  is  hard  and  brittle, 
showing,  like  the  Goldschmidt  chromium,  two  different  con- 
ditions— an  active  and  a  passive — which  may  be  artificially  pro- 
duced and  destroyed.  Taken  fresh  out  of  the  bath  it  is  active, 
but  by  lying  in  the  air  becomes  gradually  passive  and  can 
easily  be  made  active  again  by  the  methods  proposed  by 
Hittorf. 

While  being  dissolved  periodic  phenomena,  as  far  as  has 
been  determined,  do  not  take  place  during  solution,  which 
may  be  explained  by  the  assumption  that  the  periodic  phe- 
nomena are  really  caused  by  a  foreign  element  in  the  chro- 
mium, and,  therefore,  do  not  appear  with  the  very  pure  elec- 
trolytic metal. 

The  value  of  the  potential  of  electrolytic  chromium  in 
absolute  measure  when  dipped  in  normal  chromium  sulphate 
solution  was  0.258  volt,  in  normal  chromic  chloride  solution 
0.241  volt,  while  the  corresponding  values  for  zinc  were 
0.524  and  0.503  and  the  values  of  cadmium  0.162  and  0.174. 


3O  CHROMIUM  AND  ITS  COMPOUNDS. 

Active  chromium  stands,  therefore,  in  the  tension  series,  as  has 
already  been  remarked  by  Hittorf,  between  zinc  and  cadmium. 

The  voltage  required  for  decomposition  was  found  for  a  five 
times  normal  sulphate  solution  1.90  volts,  for  an  eight  times 
normal  chromic  chloride  solution  1.69  volts.  For  practical 
purposes  at  least  double  these  tensions  must  be  used. 

In  the  discussion  connected  with  this  communication 
H.  Goldschmidt  stated  that  he  likewise  had  performed  ex- 
periments for  the  precipitation  of  chromium  in  similar  appa- 
ratus. Hydrochloric  and  also  acetic  acid  solutions  were  used, 
the  latter  with  the  worst  results ;  an  iron  tube  was  used  as 
cathode,  rotated  rapidly  around  its  axis,  the  anode  was  retort 
carbon  in  acidulated  chromic  chloride  or  in  hydrochloric  acid. 
A  small  propeller  was  placed  in  the  cathode  fluid  which  was 
contained  in  a  porous  cell,  in  order  to  increase  the  circulation. 
With  current  densities  of  o.i  to  0.4  ampere  per  square  centi- 
meter of  cathode  surface  there  was  obtained  peculiar  ribbed 
or  furrowed  layers  of  metallic  chromium  several  millimeters 
thick,  but  very  brittle,  easily  detached,  and  never  quite  free 
from  oxygen ;  it  was  particularly  lustrous  upon  the  tops  of 
the  ribs.  "  Dr.  Neumann  has  gone  decidedly  further  in  his 
experiments  than  I,  since  he  has  made  exact  determinations 
of  favorable  conditions ;  moreover,  I  obtained  much  poorer 
current  output  than  Dr.  Neumann.  On  that  account  I  laid 
these  investigations  completely  to  one  side,  because  calcula- 
tions showed  that  even  if  a  higher  current  output  can  be  ob- 
tained, these  methods  would  be  too  expensive  for  commercial 
use,  at  least  as  far  as  concerns  the  manufacture  of  chromium  it- 
self, in  consequence  of  the  complicated  apparatus,  and  the  high 
current  consumption  caused  by  the  high  tension  in  the  bath." 

A  later  remark  of  the  same  person  is  worthy  of  reproduc- 
tion. "  Chromium  is,  as  is  well-known,  a  somewhat  noble 
metal  in  certain  relations  since  it  is  more  resistant  to  air  than 
nickel  and  even  better  than  cobalt.  Unfortunately  it  has  not 
been  possible  so  far  to  obtain  a  strongly  adhering  deposit  of 


BY   ELECTROLYSIS   OF   AQUEOUS   SOLUTIONS.  31 

electrolytic  chromium.  If  it  were  only  possible  to  plate 
metallic  articles  with  a  thin  sheet  of  chromium,  as  is  so  often 
done  with  nickel  (recently  electrolytic  zinc-platings  have 
also  been  successfully  produced),  it  would  be  a  great  ser- 
vice, I  believe,  to  many  branches  of  technology  and  also  to 
the  artistic  industries.  It  may  be  perhaps  a  small  step  in  the 
direction  of  reaching  that  goal  to  use  soluble  anodes  of  chro- 
mium, with  the  aid  of  which  a  constant  electrolytic  chromium 
bath  may  be  produced.  The  investigations  of  Dr.  Neumann, 
which  we  have  just  listened  to,  go  far  in  this  direction,  and 
which  may  well  form  the  foundation  of  a  technically  useful 
method  of  chromium-plating,  but  will  hardly,  as  before  re- 
marked, serve  for  manufacturing  metallic  chromium.  Appar- 
ently a  chromium-plating  upon  iron  ought  to  be  just  as  good 
as  a  zinc-plating." 

In  relation  to  the  latter  point  Ostwald  says  that  even  if  it 
was  possible  to  plate  iron  with  chromium,  the  chromium 
would  scarcely  be  permanent  since  it  would  become  active 
again  by  contact  with  this  metal.  "  Therefore  the  danger  of 
using  chromium  is  that  when  rain  falls  upon  it  hydrogen 
commences  to  evolve,  and  in  that  case  we  can  carry  the  chro- 
mium from  our  chromium-plated  bicycles  home  in  our  hand- 
kerchief." 

If,  however,  this  observation  is  worth  noticing,  the  fear  of 
such  calamitous  results  has  no  foundation.  Chromium  is  even 
in  its  active  condition  more  passive  than  zinc. 

As  already  remarked,  Hittorf  established  the  fact  that  chro- 
mium occurs  in  two  conditions,  one  active  in  which  it  lies  be- 
tween zinc  and  cadmium,  and  one  passive  in  which  it  stands 
near  to  silver ;  he  also  gives  the  conditions  under  which 
chromium  becomes  active  or  passive.  I  will  content  myself 
in  this  work  with  referring  to  the  original  article1  since  it  is 
easily  accessible  and  scarcely  falls  within  the  limits  of  our 
subject,  as  also  the  work  of  Ostwald :  "  On  the  Periodic 

1  Zeitschr.  f.  phys.  Chem.,  25,  729  (1898)  ;  3O,  481  (1899)  ;  34,  385 
(1901). 


2  CHROMIUM  AND  ITS  COMPOUNDS. 

Phenomena  when  Chromium  Is  Dissolved  in  Acids  ;m  and  the 
communication  of  Brauer:2  "  On  the  Electrolytic  Behavior  of 
Chromium  during  Solution  in  Acids." 

B.  By  the  Use  of  High  Temperatures. 

(See  also  pages  17  and  18.) 

The  obtaining  of  chromium  at  high  temperatures  by  the 
help  of  the  electric  current  was  mentioned  in  a  patent  speci- 
fication3 not  much  later  than  the  first  patent  was  taken  out  for 
the  electric  precipitation  of  chromium  from  aqueous  solutions. 
The  invention  is  concerned  with  the  melting  and  the  reduc- 
tion of  ores,  heated  by  the  assistance  of  the  electric  current 
and  used  for  the  production  of  aluminium  and  its  alloys  as 
well  as  other  metals  and  their  alloys  of  a  more  or  less  refrac- 
tory character  like  boron,  silicon,  calcium,  chromium,  titanium, 
etc.,  iron  and  steel.  If  the  ores  and  ordinary  oxides  are 
melted  and  heated  by  means  of  the  electric  current  they  are 
decomposed  and  the  oxygen  set  free  violently  attacks  the 
vessel  and  the  electrodes,  causing  considerable  expense.  This 
is  avoided  in  Wilson's  apparatus  by  the  introduction  of  a  re- 
ducing gaseous  agent  into  the  apparatus  in  such  manner  that 
the  oxygen  and  the  injurious  constituents  combine  with  the 
reducing  medium  so  that  the  electrodes  are  protected. 

When  treating  oxides,  hydrogen,  hydrocarbons  and  in  par- 
ticular ordinary  illuminating  gas,  for  instance,  may  be  used. 

The  manipulation  when  producing  aluminium  and  alumin- 
ium bronze,  which  were  the  probable  productions  to  which 
the  invention  was  applied,  was  described  at  length  and  we 
need  not  follow  this  branch  further.  It  will  suffice  to  repro- 
produce  the  most  important  patent  claims  relating  to  our  sub- 
ject. 

(i)  The  herein-described  process  of  reducing  metals  or  ores, 
consisting  in  heating  them  to  the  melting-point  by  the  elec- 
tric arc  passing  from  the  metal  or  ore  to  an  electrode  and  in- 

1  Zeitschr.  f.  phys.  Chem.,  35,  33,  204  (1900). 

2  Ibid.,  38,  441  (1901). 

3  English  Patent  No.  9,361,  June  17,  1890,  Thomas  Leopold  Wilson. 


BY  THE  USE  OF  HIGH  TEMPERATURES.  33 

troducing  a  reducing  agent  between  the  place  at  which  the 
oxygen  or  other  corrosive  agent  is  set  free,  and  the  incandes- 
cent surface  endangered  by  the  corrosion,  in  order  to  protect 
the  latter  from  destruction,  substantially  as  described. 

(2)  The  herein-described  process   of  reducing    metals   or 
ores  consisting  in  heating  them  to  melting  by  an  arc  passed 
between  the   metal  or  ore  and  an  electrode  above  and  the  in- 
troduction of  a  reducing  agent  downwards  into  the  arc  be- 
tween the  place  at  which  the  oxygen  or  any  other  destructive 
agent  is  set  free  and  the  incandescent  electrode  surface  which 
is  endangered,  in  order  to  protect  the  latter  from  destruction, 
substantially  as  described. 

(3)  The    herein-described  reduction   process  for  metals  or 
ores,  consisting  in  heating  them  to  melting  by  means  of  an 
electric  arc  passed  between  the  metal  or  ore  and  an  electrode 
above,  and  the  introduction  of  a  reducing  agent  downwards 
into   the   arc   by   passing   it    through   the  electrode  shown, 
whereby  the  gas  distributes  itself  uniformly  around  the  incan- 
descent end  of  the  electrode  and  rising  in  a  protecting  stream, 
surrounds  the  electrode  on  all  sides,  as  described  in  the  speci- 
fications and  for  the  purpose  designated. 

(4)  The  herein-described  reduction  process  for  metals  or 
ores  consisting  in  subjecting  them  to  the  heat  of  the  electric 
arc  passing  from  the  positive  electrode  underneath  the  metal 
or  ore  to  the  negative  electrode  above   the  same,  introducing 
a  reducing  gas  into  the  arc  through  the  said  negative  elec- 
trode, whereby  the  gas  is  introduced  into  the  center  of  the 
current  of  gas  which  is  projected  from  the  positive  electrode 
beneath,  against  the  negative  electrode,  and  the  gas  so  protects 
the  electrode  from  destruction,  substantially  as  described. 

(5)  The     herein-described    process    for   the   reduction   of 
aluminium  and  other  metals  from  refractory  ores  and  for  the 
production  of  alloys  of  these  metals,  consisting  in  the  melting 
of  the  ores  by  means  of  the  electric  arc  in  the  presence  of  the 
melted  bath  of  the  base  metal  to  be  alloyed  and  passing  the 
electric  current  through   the  said  bath  as  anode  to  a  carbon 


34  CHROMIUM  AND  ITS  COMPOUNDS. 

cathode  placed  above  it,  in  the  presence  of  a  reducing  agent 
which  can  unite  with  the  oxygen  set  free  or  any  other  corro- 
sive elements  resulting  from  the  decomposition  of  the  ore, 
substantially  as  previously  described. 

(6)  The  improved  electric  furnace  for  the  reduction  of  re- 
fractory ores  consisting  of  the  melting  crucible  connected 
with  the  current  conductor  which  serves  to  conduct  the  cur- 
rent to  the  interior  of  the  crucible,  a  tube-formed  electrode 
projecting  downwards  into  the  said  crucible  and  a  source  of 
reducing  gas  in  connection  with  the  electrode  through  which 
the  gas  enters  the  crucible,  in  order  to  surround  the  white-hot 
end  of  the  electrode  and  to  protect  it,  substantially  as  de- 
scribed. 

The  patent1  taken  out  in  the  year  1893  °y  the  nrm  °f 
Friedrich  Krupp,  of  Essen,  has  essentially  for  its  principal 
object  the  manufacture  of  chromium  ;  as  the  raw  material  for 
the  manufacture  of  pure  chromium,  there  is  used  an  anode  of 
impure,  carbonaceous,  crude  metal  in  the  ordinary  commercial 
form ;  if  an  electric  current  is  led  through  it,  using,  for  in- 
stance, molten  sodium  chloride  as  electrolyte,  the  anode  is 
changed  into  metallic  chloride  by  the  chlorine  evolved,  which 
dissolves  in  the  melt,  while  at  the  cathode  metallic  sodium  is 
evolved.  The  latter  must  be  rendered  harmless  since  it  would 
precipitate  again  the  metal  from  the  metallic  chloride  by 
simple  replacement ;  to  avoid  this  the  patent  provides  various 
devices. 

The  negative  pole  may  be  surrounded  by  a  clay  cell  or  an 
unattackable  diaphragm  may  be  brought  between  the  two 
poles,  or  the  electrolysis  may  be  performed  in  a  U-shaped 
tube  of  refractory  material.  The  sodium  evolved  may  also  be 
vaporized  by  the  use  of  a  high  enough  temperature,  or  changed 
back  again  to  chloride  by  the  use  of  a  current  of  chlorine  gas. 

As  soon  as  a  sufficient  amount  of  metal  has  been  converted 
into  chloride  at  the  anode  any  sodium  or  sodium  oxide  re- 
maining at  the  cathode  is  removed  in  a  suitable  manner,  and 
1  German  Patent  81,225,  June  i,  1893. 


BY  THE  USE  OK  HIGH  TEMPERATURES.  35 

by  further  electrolysis  the  pure  metal  or  alloy  is  obtained, 
while  at  the  same  time  fresh  metal  is  continually  dissolved  at 
the  anode  and  the  composition  of  the  bath  remains  constant. 
By  using  impure  ferro-chromium  as  an  anode,  pure  ferro-chro- 
mium  is  obtained  at  the  cathode ;  the  same  process  may  be 
employed  for  other  metals  and  alloys. 

In  place  of  sodium  chloride  other  halogen  salts  melt- 
ing at  a  red  heat  may  be  used,  and  in  case  they  can  be  ob- 
tained the  halogen  compounds  of  the  metallurgical  products 
being  electrolyzed. 

The  patent  claim  reads  :  An  electrolytic  process  for  the 
manufacture  of  pure  chromium  and  manganese  and  pure 
alloys  of  the  same  by  electrolyzing  compounds  rendered  fluid 
by  heat  characterized  by  using  the  carbonaceous  metals  and 
alloys  of  the  two  named  metals  as  anodes  in  an  easily  fusible 
bath  of  halogen  compounds,  and  precipitating  out  pure  metals 
and  pure  alloys  at  the  cathode. 

The  manufacture  of  pure  chromium  does  not  succeed  in  the 
manner  described  without  further  precautions,  since  the 
metallic  impurities  of  the  crude  metal  will  be  found  for  the 
most  part  in  the  metal  precipitated  at  the  cathode. 

The  idea  of  "  purity"  seems  to  be  somewhat  indistinct  in 
the  patentee's  mind,  since  the  mere  absence  of  carbon  seems 
to  be  regarded  as  sufficient  warrant  for  calling  the  metal  pre- 
cipitated "  pure."  What  has  just  been  said  regarding  chro- 
mium itself  is  true  also  of  its  alloys  since  besides  the  metals 
to  be  alloyed,  other  metals  were  separated  out  of  the  electro- 
lyte if  present. 

With  constant  use  the  bath  would  further  become  very  im- 
pure ;  it  is  not  clear  that  the  solution  of  the  anode  would  go 
forward  easily  and  without  a  considerable  increase  of  voltage. 

Much  better  results  'may  be  obtained  by  the  manner  de- 
scribed by  Moissan  in  two  communications.1  He  heated  a 

1  Compt.  rend.,  116,  349  (1893)  and  119,  185  (1894).  See  also  Ann. 
chim.  phys.,  78,  559  (,1896).  A  form  of  furnace  which  is  described  in 
Compt.  rend.,  117,  679,  in  which  the  raw  material  is  passed  into  the  melt- 
ing zone  through  a  hollow,  suitably  inclined,  carbon,  tube  terminating  about 
i  cm.  underneath  the  arc. 


36  CHROMIUM  AND  ITS  COMPOUNDS. 

mixture  of  calcined  chromic  oxide  and  carbon  in  the  electric 
furnace  and  obtained  a  shining  and  completely  melted  mate- 
rial. Using  350  amperes  and  50  volts,  the  operation  was 
imished  in  eight  to  ten  minutes ;  the  charge  had  a  weight  of 
100  to  no  grams.  With  30  volts  and  50  amperes  he  obtained 
a  button  of  TO  grams  in  thirty  to  forty  minutes. 

These  buttons  stuck  to  the  crucible  and  contained  more  or 
less  carbon  according  to  the  composition  of  the  original  mix- 
ture. The  carbon  content  of  the  pieces  analyzed  varied  be- 
tween 8.6  and  12.8  per  cent.  The  mass  was  purified  by  a 
further  operation :  It  was  broken  into  large  pieces,  put  into  a 
carbon  crucible  carefully  lined  with  chromic  oxide,  and  covered 
with  chromic  oxide.  The  mixture  was  then  subjected  to  the 
heat  of  the  electric  arc  by  which  the  oxide  upon  the  surface  and 
also  the  metal  melted  and  the  latter  gradually  lost  its  carbon 
content ;  at  least  in  heating  in  a  current  of  chlorine  no  traces 
of  carbon  remained  behind. 

The  natural  chrome  iron  ore,  FeO.Cr2O  ,  can  be  reduced 
in  the  same  manner  as  chromic  oxide  forming  a  chromium- 
iron  alloy  ;  the  material  is  broken  to  a  coarse  powder,  an  ap- 
propriate quantity  of  carbon  added  and  the  whole  heated  in 
the  electric  furnace.  Moissan  operated  with  2  kilograms 
of  ore  and  1000  amperes  of  current,  at  60  volts,  and  obtained 
in  a  few  minutes  completely  melted  lumps  of  ferro-chrome  of 
the  following  composition  :  Chromium  60.9  per  cent,  iron 
31.6  per  cent.,  total  carbon  6.1  per  cent.,  silicon  i.i  per  cent. 
He  proposed  to  use  this  product  for  the  manufacture  of  alka- 
line bichromates  by  bringing  the  coarsely  pulverized  material 
into  a  bath  of  molten  potassium  or  sodium  nitrate;  there  would 
result  insoluble  iron  oxide  and  soluble  alkaline  chromates. 

In  his  second  communication,  Moissan  explains  that  the 
chromium  made  in  the  way  just  described,  "  is  saturated  with 
oxygen,  and,  therefore  from  the  standpoint  of  the  metallurgist 
was  burned"  He  attempted  on  this  account  another  method 
of  purification,  by  melting  the  metal  in  quantities  of  one-half 
to  one  kilogram  with  lime,  this  taking  up  the  larger  part  of 


BY  THE  USE  OF  HIGH  TEMPERATURES.  37 

the  carbon  to  form  calcium  carbide,  but  leaving  in  the  chro- 
mium the  remainder  of  it,  1.5  to  1.9  per  cent,  as  beautiful 
cubical  and  octahedral  crystals,  which  he  could  not  remove. 
"  We  observe,  in  fact,  that  the  reverse  reaction  would  take  place 
in  the  presence  of  the  fluid  lime  and  the  furnace  gases,  if  the 
chromium  was  sufficiently  pure.  Thus  the  whole  metal  would 
be  transformed  into  the  crystallized  double  oxide  of  chromium 
and  lime."1 

Finally  this  easily  formed  double  oxide  was  used  for  puri- 
fication ;  a  lime  crucible  was  lined  with  it  and  the  carbonized 
metal  melted  in  it.  After  cooling  there  was  obtained  a 
brilliant  metal  which  could  be  filed  and  polished  easily  and 
showed  on  analysis  no  trace  of  carbon. 

Borchers  remarked  .on  this  process  :2  "  Moissan  has  solved 
this  question  of  the  refining  in  a  very  skilful  way  by  bring- 
ing over  for  the  purpose  of  refining  chromium,  the  principle 
of  the  basic  Siemens-Martin  furnace  for  making  steel.  By 
heating  lime  with  chromic  oxide  he  has  manufactured  a  basic 
material  which  not  only  serves  for  oxidation  but  for  the  pur- 
pose of  slagging  off  the  impurities.  By  lining  the  hearth  of 
the  electric  furnace  with  this  calcium  chromite  and  melting 
thereupon  the  carbonaceous  and  siliceous  metal  the  impurities 
are  entirely  oxidized  and  removed  by  the  chromic  oxide  just 
as  occurs  to  impurities  in  the  Martin  steel  process  by  the  action 
of  iron  oxide. 

No  further  data  are  known  about  the  cost  of  this  process. 
The  commercial  practicability  is  scarcely  to  be  doubted,  but 
the  cost  could  be  considerably  reduced  by  producing  the  crude 
chromium  as  a  carbonaceous  metallic  powder  either  in  cruci- 
ble furnaces  or  in  electrolytic  resistance  furnaces  in  order  to 
save  the  heat  necessary  for  melting  it. 

At  this  point  Moissan  remarks  that  melted  lime  can 
also  be  used  for  the  refining  of  commercial  ferro-chromium  in 
the  electric  furnace.  He  has  for  instance  found  that  commer- 

1  Moissan  :  "  Der  Elektrische  Oefen,"  1897,  p.  196. 
'2  "Elektrometallurgie,"   2nd  Ed.,  p.  347. 


38  CHROMIUM  AND  ITS  COMPOUNDS. 

cial  ferro-chromium  with  7.3  per  cent,  of  carbon,  contained 
only  5  per  cent.,  after  having  been  melted  once  under  a  layer 
of  melted  lime  and  after  the  second  melting  only  o.i  per  cent.; 
by  using  this  commercial  product  a  considerable  amount  of 
chromium  can  be  introduced  into  steel  without  raising  its 
carbon  content.  He  is  of  the  opinion  that  these  experiments 
might  probably  be  utilized  on  an  industrial  scale. 

Since  the  properties  of  pure  chromium  are  of  importance, 
the  following  data  of  Moissan's  are  repeated,  especially  since 
they  contradict  part  of  the  information  found  in  the  text-books. 

The  density  is  6.92  at  20°  C.  It  burns  quickly  but  with  a 
much  more  active  discharge  of  sparks  than  iron  when  brought 
into  the  blue  point  of  the  blowpipe  flame ;  the  residue  is  a 
round  piece  of  melted  chromic  oxide.  .  It  is  worth  while  re- 
membering, moreover,  that  the  carbonaceous  material  burns 
much  more  difficultly  although  it  melts  lower ;  the  melting- 
point  of  pure  chromium  is  above  that  of  platinum. 

Molten  chromium  in  the  electric  furnace  is  a  mobile  shin- 
ing fluid  similar  to  mercury ;  it  can  be  cast  into  a  mould.  By 
using  1000  amperes  and  70  volts,  10  kilograms  of  (not  quite 
pure)  chromium  can  be  melted  at  one  time,  in  a  suitable  fur- 
nace. 

Quite  pure  chromium  containing  no  iron  exerts  no  influ- 
ence on  the  magnetic  needle.  It  has  great  capacity  for  taking 
a  polish,  and  its  hardness  is  less  than  that  of  quartz  ;  glass  is 
scratched  by  it  with  great  difficulty.  Carbonaceous  chromium 
is  much  harder.  The  carbide  CCr4  scratches  quartz  with 
difficulty,  the  carbide  C2Cr3  scratches  topaz,  and  the  finely 
granular  metal,  whose  carbon  content  is  between  1.5  and  3. 
per  cent.,  can  only  be  worked  by  cutting  stones  charged  with 
diamond  dust. 

Carbonic  acid  and  moisture  have  no  appreciable  influence 
upon  the  crude  chromium  at  ordinary  temperatures,  while 
pure,  well-polished  chromium  suffers  a  superficial  light  oxida- 
tion. In  general,  it  can  be  designated  as  unchangeable  in  the 
air.  Heated  in  oxygen  to  2000°  it  burns  with  evolution  of 


BY  THE  USE  OF  HIGH  TEMPERATURES.  39 

sparks.  If  filings  are  heated  to  700°  in  sulphur  vapor  they 
glow  and  are  changed  to  chromic  sulphide. 

If  a  mixture  of  pure  chromium  and  carbon  is  heated,  crys- 
talline needles  of  the  carbide  CCr  are  formed  with  a  violent 
deflagration,  while  at  the  temperature  of  the  electric  furnace 
C2Crs  results. 

Boron  and  silicon  unite  with  chromium  at  the  heat  of  the 
electric  furnace  to  finely  crystalline  compounds  of  great  hard- 
ness and  resistance  to  chemical  reagents. 

Gaseous  hydrochloric  acid  acts  on  it  at  a  red  heat,  forming 
chromous  chloride.  Aqueous  hydrochloric  acid  attacks  the 
metal  very  slowly  when  cold,  faster  when  warm  ;  used  as  an 
anode  it  dissolves  even  in  dilute  acids  which  otherwise  would 
attack  it  only  at  boiling.  Further  data  on  the  behavior  of 
chromium  towards  acids  and  its  use  as  electrodes,  about  its 
active  and  passive  conditions,  etc.,  were  published  a  year  later 
by  Hittorf  (see  page  29). 

At  1200°  chromium  is  attacked  by  a  current  of  hydrogen 
sulphide  and  converted  entirely  into  a  sulphide  of  crystalline 
appearance ;  in  carbonic  acid  it  covers  itself  at  this  tempera- 
ture superficially  with  a  layer  of  green  chromic  oxide  mixed 
with  carbon ;  carbon  dioxide  attacks  it,  forming  superficially 
a  layer  of  Cr2O3  while  the  metal  absorbs  carbon,  a  circum- 
stance which  explains  the  difficulties  which  are  met  with 
when  one  tries  to  refine  chromium  in  the  lime  crucible. 

Chromium  is  not  sensibly  attacked  by  melted  caustic  potash; 
on  the  other  hand  it  burns  with  beautiful  illumination  in  con- 
tact with  melted  potassium  nitrate  or  still  better  at  a  red  heat 
with  potassium  chlorate. 

Finally,  the  interesting  properties  of  some  alloys  are  men- 
tioned. Pure  copper  containing  0.5  per  cent,  chromium  has 
nearly  double  as  much  electrical  resistance  and  is,  when  well 
polished,  more  resistant  to  damp  air  than  without  this  addi- 
tion. 

Two  Russians,  A.  Koryscheff  and  S.  Demmenie,  together, 


40  CHROMIUM  AND  ITS  COMPOUNDS. 

in  the  year  1896,  took  out  the  English  patent1  for  a  very  gen- 
eral process  for  the  direct  manufacture  of  iron,  chromium 
and  analogous  metals  from  their  oxygen,  sulphur,  arsenic,  etc., 
compounds,  and  since  they  use  electrical  energy  we  will  re- 
produce the  more  important  part  of  it  from  their  very  com- 
prehensive patent  specifications  which  contain  many  draw- 
ings. We  need  not  go  further,  however,  into  the  considera- 
tion of  their  metallurgical  furnace  likewise  protected  by  En- 
glish patents. 

The  two  authors  emphasize  that  the  study  of  "pyrochem- 
ical  solutions,"  that  is,  the  solutions  in  which  one  body  is  dis- 
solved in  another  rendered  fluid  by  heat,  leads  to  the  convic- 
tion that  the  dissolved  bodies,  be  they  of  simple  or  of  combined 
chemical  nature,  have  acquired  a  gas-like — that  is,  a  very 
diluted  condition.  The  degree  of  "dilution"  (rarefaction)  can 
be  increased  in  three  ways :  First,  by  raising  the  temperature  ; 
second,  by  the  action  of  chemical  agents ;  and  third,  by  the 
help  of  electricity.  Naturally,  all  three  aids  to  this  end  may 
be  used  alone  or  in  combination  with  each  other ;  so  may,  for 
instance,  iron  oxide  dissolved  in  molten  silicates  be  reduced 
either  by  raising  the  temperature  to  the  dissociation  point  or 
at  a  lower  temperature  by  the  help  of  chemical  reagents  or  by 
electricity. 

After  this  somewhat  fantastic  presentation  they  explain  the 
main  idea  of  their  invention,  that  of  performing  the  decom- 
position or  the  reduction  of  metallic  compounds  by  bringing 
them  into  the  condition  of  pyrochemical  solutions,  in  order 
to  then  subject  them  to  the  action  of  heat,  chemical  and  elec- 
trical energy  ;  they  then  affirm  that  this  pyrochemical  pro- 
cess is  applicable  to  all  metals  and  alloys. 

Since  a  pyrochemical  solution  is  aimed  at,  great  care  must 
be  taken  that  the  ores,  gangue  and  furnace  lining  are  so  chosen 
that  a  fluid  mass  containing  the  metal  will  result. 

Electrical  energy  can  be  called  upon  as  explained,  as  sup- 
plementary to  the  influence  of  heat  and  chemical  action,  but 

1  English  Patent  6,654  ;  March  26,  1896. 


BY  THE  USE  OF  HIGH  TEMPERATURES.  41 

its  office  when  so  used  is  an  entirely  different  one  from  elec- 
trolysis ;  it  acts  here  upon  materials  which  are  already  in  the 
condition  of  "tension,"  so  that  only  the  smallest  assistance  is 
required  from  it  in  order  to  complete  the  dissociation. 

The  electric  energy  can  be  used  either  as  dynamic  or  static. 
In  practice  it  is  advantageous  to  use  transformers  for  the  ob- 
taining of  very  high  tensions,  and  to  connect  the  anodes  with 
the  slag  and  the  cathodes  with  the  hearth  of  the  furnace 
which  in  this  case  is  made  of  a  conductor  such  as  graphite. 

The  current  produced  in  the  transformer  is  so  regulated 
that  an  "electric"  discharge  passes  from  one  side  of  the  elec- 
trodes, and  a  dark  discharge  from  the  other.  For  this  pur- 
pose suitable  resistances  are  put  into  the  circuit  as  well  as  a 
quick-working  interrupter  to  avoid  the  development  of  the 
small  high-tension  closing  currents. 

The  above  will  do  for  characterizing  this  new  invention  ; 
further  criticism  is  not  necessary.  Of  the  patent  claims,  the 
following  concern  us.  They  claim  : 

(i)  A  new  process  for  the  direct  production  of  metals  and 
their  alloys  from  their  ores,  characterized  by  the  conversion 
•of  the  whole  charge  into  the  melted  condition  in  such  manner 
that  the  metallic  compounds  are  dissolved  "  pyrochemically  " 
in  the  rest  of  the  mass. 

(5)  In  the  manufacture  of  metals  from  their  ores  according 
to  the  methods  described  under  (i),  the  use  of  chemical  reagents 
in  the  form  of  pyrochemical  solutions  as  a  supplement  to  the 
thermic  energy. 

(6)  For  the  manufacture  or  formation  of  pyrochemical  so- 
lutions (see  5)  the  introduction  of  carbon  into  the  charges  in 
quantities  of  1/5  to   1/40  of  that  necessary  fof  the  conversion 
of  the  oxygen  present  in  the  oxide  into  carbon  dioxide. 

(7)  The  combination  of  the  process  described  under  (i)  with 
the  use  of  electrical  currents  as  supplemental   to  thermic  and 
chemical  energy  as  described. 

(8)  In  the  process  as  described  the  use  of  electrical  energy 
in  the  form  of  dark  discharges  of  very  high  tension,  which  are 


42  CHROMIUM  AND  ITS  COMPOUNDS. 

rendered  possible  practically  by  the  including  in  the  circuit 
of  suitable  resistances  for  the  purposes  of  choking  the  contact 
currents  of  the  transformer  or  by  means  of  the  acoustic  inter- 
rupter which  produces  alternating  current  of  very  high  tension 
and  extremely  high  frequency,  as  described. 

The  German  patent  of  Aschermann1  is  concerned  only  with 
the  reduction  of  chromium.  An  air-tight  electrical  melting 
apparatus  of  cast  steel,  containing  an  exactly-fitting  graphite 
crucible  to  receive  the  bath  into  which  a  movable  non-porous 
electrode  passes,  is  used.  It  is  charged  with  a  mixture  of 
chromic  oxide  and  antimony  sulphide,  in  the  proportion  of 
10:23  or  also,  not  so  strongly  recommended,  however,  with  a 
mixture  of  chromic  oxide,  sulphur  and  pure  antimony  in  the 
proportions  of  i o  :  10  :  23;  the  apparatus  is  thereupon  closed  air- 
tight and  a  relatively  gentle  current  of  20  to  2  5  amperes  passes 
through.  This  suffices  to  melt  the  mass  and  cause  the  reaction 
in  the  crucible.  The  process  proceeds  with  considerable  de- 
velopment of  heat.  On  opening  the  apparatus  there  is  found, 
in  the  upper  part,  antimony  oxide  as  an  amorphous  deposit,  a 
very  small  part  of  which  may,  however,  be  crystalline,  also 
antimony  sulphide  and  traces  of  chromic  oxide,  but  on  the  other 
hand  the  crucible  contains  a  molten  mass  of  evidently  crys- 
talline structure  consisting  of  metallic  chromium  in  combina- 
tion with  the  excess  of  antimony.  The  removal  of  the  anti- 
mony by  repeated  remeltings  is  difficult  and  costly  ;  it  is  much 
simpler  and  cheaper  to  break  up  the  mass  and  heat  it  over  an 
open  fire.  The  antimony  volatilizes  at  a  white  heat  and  me- 
tallic chromium  remains  behind,  since  chromium  itself  only 
volatilizes  at  temperatures  above  2000°. 

It  is  worth  remarking  in  connection  with  this  process  that 
the  electric  current  seems  to  be  used  only  for  starting  the  re- 
action. A  small  part  of  the  mass  is  heated  by  the  help  of  the 
heat  developed  by  the  current  to  the  temperature  of  reaction 
and  the  heat  generated  by  the  decomposition  then  suffices  to 
continue  the  reaction  throughout  the  whole  mass  and  to  bring 

1  German  Patent  93,744,  June  30,  1896. 


BY  THE  USE  OF  HIGH  TEMPERATURES.  43 

it  to  fusion.  The  cost  of  the  electrical  energy  is,  therefore,  al. 
most  negligible.  If  the  reaction  takes  place  as  is  claimed,  and 
if  the  separation  of  the  chromium  from  the  antimony  proceeds 
in  such  a  simple  manner  as  the  description  would  lead  one  to 
believe,  then  this  process  must  be  described  as  comparatively 
simple  and  applicable  for  the  manufacture  of  large  quantities 
of  chromium. 

The  patent  claim  reads  :  Obtaining  of  metallic  chromium 
from  chromic  oxide  by  the  agency  of  antimony  sulphide  in 
the  electric  furnace. 

In  a  supplementary  patent1  the  author  extends  his  process 
to  other  metals  and  to  metallic  alloys.  He  makes  in  this  con- 
nection the  following  remarks  which  are  of  interest,  particu- 
larly for  the  obtaining  of  pure  chromium  and  part  may  be  re- 
garded as  an  explanation  of  the  process  described  in  the 
principal  patent. 

"  The  manufacture  of  pure  metals  in  electric  melting  fur- 
naces from  their  oxides  offers  great  difficulties  if  the  metals 
have  a  great  capacity  for  dissolving  carbon.  There  is  then 
-obtained  either  a  carbide  or  a  metal  highly  contaminated  with 
carbon.  It  is  necessary  to  use  an  easily  fusible  metal  as  an 
addition  which  will  unite  with  the  reduced  metal  in  the  nas- 
cent state  and  prevent  it  thereby  from  taking  up  carbon. 
But  this  alone  is  not  sufficient.  To  obtain  the  metal  as  free 
as  possible  from  carbon  it  is  further  necessary  that  the  reduc- 
tion proceed  quickly  and  that  it  be  operated  by  the  smallest 
current  possible.  Quite  aside  from  the  cost  of  production, 
this  is  an  important  requisite.  It  is  not  possible  to  obtain  the 
reduced  metal  pure  if  strong  currents  are  used  or  by  a  lengthy 
application  of  the  arc.  The  fluxes  volatilize  and  in  their 
place  carbon  is  absorbed  by  the  metal.  Finally  the  metal 
obtained  will  volatilize  itself,  and  there  will  remain  behind 
only  carbon  in  the  form  of  graphite.  The  metal  added  has 

1  D.  R.  P.  No.  94,405  of  24th  of  November,  1896.  Extreme  life  until 
June  29,  1911.  The  English  Patent  No.  859,  taken  out  by  Aschermann,  Jan- 
uary 12,  1897,  contains  the  substance  of  both  the  German  patents  cited. 


44  CHROMIUM  AND  ITS  COMPOUNDS. 

either  none  or  only  a  very  slight  influence  upon  the  course  of 
the  reduction;  it  serves  more  as  a  means  of  protection  against 
the  taking  up  of  carbon.  If  a  metallic  sulphide  is  used  as 
the  addition,  the  reaction  takes  place  quickly  and  with  a 
much  smaller  expenditure  of  electrothermal  energy.  It  is 
therefore  the  sulphur  which  influences  favorably  the  course  of 
the  reduction." 

The  manufacture  of  metallic  compounds  in  the  way  de- 
scribed is  stated  to  be  of  great  importance.  For  instance,  ac- 
cording to  this  process,  ferro-chrome  can  be  made  by  the  melt- 
ing together  of  10  parts  of  iron  sulphide  and  9  parts  of  chromic 
oxide ;  also  for  this  reaction  a  comparatively  small  amount  of 
electrical  energy  suffices. 

Patent  Claim. 

A  process  of  obtaining  metallic  alloys  and  pure  metals  by 
the  electrical  heating  of  a  mixture  consisting  of  the  oxide  of 
one  and  the  sulphide  of  another  metal  or  the  oxide  of  the 
metal  and  the  sulphide  of  a  non-metal,  or  from  one  oxide  of  a 
non-metal  and  the  sulphide  of  the  metal  with  the  exclusion  of 
the  process  of  manufacture  of  chromium  described  in  patent 

No.  93,744- 

The  foregoing  compilation  exhausts  the  processes  which 
endeavor  to  manufacture  chromium  by  the  direct  application 
of  the  electric  current.  I  cannot,  however,  close  this  chapter 
without  thinking  of  the  processes  which  manufacture  these 
metals  by  the  indirect  use  of  the  electric  current  such  as  by 
reducing  chromium  from  its  compounds  by  means  of  alumin- 
ium, or  magnesium  or  calcium  carbide,  which  substances  are 
indeed  to-day  manufactured  by  electrolytic  processes.  Since, 
moreover,  these  processes  are  likely  to  become  important  and 
are  already  beginning  to  be  so  at  present,  it  is  advisable  to 
present  the  patent  literature  on  this  subject,  which  may  not 
be  easily  accessible  to  everybody. 

The  first  to  be  mentioned  is  the  proposition  to  obtain  chrom- 
ium in  the  already-mentioned  manner,  made  by  J.  Vautin.1 

1  English  Patent  8,306,  April  26,  1894. 


BY  THE  USE  OF  HIGH  TEMPERATURES.  45 

His  patent  is  dated  April  26,  1894.  He  alludes  to  the  great 
affinity  of  the  finely  divided  metallic  aluminium  for  oxygen 
and  sulphur  by  means  of  which  other  metals  may  be  reduced 
from  their  oxides  and  sulphides  and  in  every  case  from  their 
sulphates  while  the  heat  generated  in  the  decomposition  keeps 
in  fusion  the  difficultly  fusible  metals  and  brings  the  reduced 
metal  mostly  into  a  compact  molten  condition.  The  metal 
obtained  is  free  from  aluminium  and  naturally  also  from 
carbon. 

For  the  reduction  there  is  used  a  vessel  lined  with  refrac- 
tory material  like  magnesia  into  which  the  substance  to  be 
reduced  mixed  with  very  finely  divided  aluminium  is  placed. 
Stress  is  laid  upon  the  very  fine  division  of  the  aluminium, 
since  on  this  depends  the  obtaining  of  the  reduced  metal  con- 
taining no  admixture  of  aluminium:  The  resulting  slag  may 
be  in  certain  cases  made  more  fusible  by  the  addition  of  fluxes 
like  cryolite  and  fluorite ;  potassium  chloride  and  sodium 
chloride  may  also  be  used. 

The  equation  of  the  reduction  is  given  as  CraO  -f  A12  = 
Cr2  -f  A12O3,  which  makes  it  evident  that  the  normal  propor- 
tions by  weight  were  used  for  the  mixture,  but  this  is  not 
particularly  specified.  An  excess  of  aluminum  will  not  hurt, 
since  it  is  easily  burned  out  or  volatilized,  and  in  this  manner 
does  not  get  into  the  reduced  metal.  In  general,  an  excess  of 
oxide  or  sulphide  is  to  be  recommended.  The  reaction  is  com- 
plete "  as  soon  as  the  temperature  is  reached  at  which  the 
aluminium  unites  with  the  oxygen  or  sulphur." 

The  patent  claim  reads  : 

(1)  The  manufacture  of  chromium,  iron,  tungsten,  titanium, 
molybdenum,  nickel,  cobalt,  uranium,  vanadium,   and  beryl- 
lium  by  the   treatment   of  their  oxides  and  sulphides  with 
aluminium,  in  the  finely  divided  or  powdered  condition  at  high 
temperatures,  as  described. 

(2)  In  the  herein-described  process  of  reducing  metals  from 
their  oxides  and  sulphides  the  use  of  metallic  aluminium  in 


46  CHROMIUM  AND  ITS  COMPOUNDS. 

finely  divided  or  powdered  condition  as  the  reducing  agent,  as 
described. 

The  German  patent1  of  the  firm  of  Th.  Goldschmidt,  of 
Essen,  has,  in  the  main,  the  same  contents  except  that  it  is 
limited  especially  to  the  manufacture  of  chromium.  It  states 
that  the  attempts  to  reduce  the  oxides  of  manganese  by  alumin- 
ium have  not  been  practically  successful,  because  the  result- 
ing slag,  A12O  ,  with  an  admixture  of  manganese  oxides,  is 
extremely  fluid  and  highly  capable  of  dissolving  the  materials 
of  which  crucibles  are  made.  The  case  is  not  so  difficult  with 
chromium,  because  the  chromium-carrying  alumina  slag  does 
not  attack  the  crucible  walls  and  is  so  viscous  that  it  will  not 
pass  through  cracks  of  considerable  size,  "  but  in  fact  makes 
its  own  containing  vessel  by  the  formation  of  a  solidified  layer 
or  coating."  "  The  process  is  carried  out  by  mixing  the 
chromium  oxide  with  a  small  excess  above  the  theoretically 
required  quantity  of  finely  divided  aluminium,  and  this  mix- 
ture heated  in  a  suitable  furnace,  as  for  instance  a  reverberatory 
furnace  or  in  crucibles,  until  the  reaction  begins,  whereupon 
there  is  formed  a  metallic  mass  and  a  layer  of  melted  alumina 
lying  upon  it." 

Patent  Claim. 

A  process  for  the  manufacture  of  molten  reguline  metallic 
chromium  characterized  by  heating  a  mixture  of  aluminium 
with  chromic  oxide  in  a  crucible  or  furnace  by  external  heat 
until  the  reaction  begins,  whereby  a  metallic  mass  of  molten 
chromium  is  formed  and  upon  it  a  layer  of  melted  chro- 
miferous  alumina. 

In  both  the  patents  alluded  to,  the  commencement  of  the 
reaction  is  brought  about  by  heating  the  whole  mixture  ex- 
ternally up  to  the  temperature  of  reaction.  Since  the  reac- 
tion is,  however,  strongly  exothermic  (evolving  heat)  it  is 
therefore  evidently  sufficient  to  heat  only  a  part  of  the  mass 
either  by  the  blowpipe  flame  or  an  incandescent  body  heated 
electrically,  or  in  any  other  way,  and  so  bring  it  locally  to  the 
1  German  Patent  112,586,  Jan.  20,  1895. 


BY  THE  USE  OF  HIGH  TEMPERATURES.  47 

reaction  temperature.  The  heat  set  free  by  the  reaction  will 
suffice  to  propagate  it  throughout  the  whole  mass.  As  I  have 
already  mentioned,  a  similar  manner  of  ignition  appears  in 
Aschermann's  process  (page  42). 

The  same  idea  is  again  worked  out  by  Goldschmidt  and 
Vautin  in  two  new  patents. 

The  first1  begins  with  the  following  sentence  :  "  The  object 
of  the  present  patent  is  a  process  for  the  manufacture  of  pref- 
erably difficultly  fusible  metals  and  their  alloys  with  each 
other  and  with  metalloids.  These  metals  or  metalloids  are 
separated  out  of  their  oxygen  and  sulphur  compoiinds  by  a 
process  of  fusion,  either  alone  or  several  simultaneously  by 
the  action  of  aluminium  or  a  mixture  of  aluminium  and  mag- 
nesium." 

It  is  seen  that  the  process  is  not  here  limited  to  chromium 
but  rendered  general,  and  that  magnesium  is  added  to  alumin- 
ium as  a  means  of  reduction.  Further  attention  is  drawn  to 
the  fact  that  the  reaction  is  exothermic  and  a  new  manner  of 
ignition  is  proposed.  It  is  worth  noticing  that  the  external 
heating  of  the  mixture  is  now  designated  as  particularly  im- 
practicable. "  Since  if  the  mixture  is  heated  all  at  once  to 
the  temperature  of  ignition  it  will  react  with  explosive  violence 
and  it  has  been  found  impossible  to  manufacture  the  metals 
or  alloys  of  the  same  commercially  in  this  way." 

It  is  not  necessary  to  enter  further  into  the  details  of  these 
patents  ;  they  are  clearly  mentioned  in  the  patent  claims.  We 
may  add,  however,  that  continuous  working  is  described,  for 
instance,  by  taking  out  the  metal  formed  at  the  bottom  of  the 
reaction  vessel  from  a  tap-hole,  and  allowing  the  slag  to  flow 
from  a  corresponding  opening  higher  up,  and  continuing  the 
process  in  this  manner  by  the  addition  of  new  reaction  ma- 
terial. 

If  it  is  desired  to  obtain  an  alloy,  one  may  take  a  mixture 
of  the  oxides  of  the  metals  concerned  or  of  their  sulphides  or 
evidently  adding  a  part  in  the  metallic  form  to  the  mixture  ;  if 

1  German  Patent  96,317,  March  13,  1895. 


48  CHROMIUM  AND  ITS  COMPOUNDS. 

it  is  wished  that  the  alloy  contain  aluminium  the  latter  is  used 
in  excess,  while  by  using  an  excess  of  the  other  metallic  com- 
pounds, metals  are  obtained  free  from  aluminium.  The  fol- 
lowing patent  claims  are  reproduced  : 

(1)  An  apparatus  for  the  manufacture  of  metals  and  metal- 
loids or  alloys  of  the  same  with  each  other  by  reducing  their 
oxygen  or  sulphur   compounds   by  means  of   aluminium  or 
aluminium  and  magnesium,  the  process   being  characterized 
by  the  fact  that  the  whole  mixture  to  be  ignited  is  not  ignited 
at  once  but   only  a  part,   whereby  the  exothermic  reaction 
propagates  itself   from  that  part  to  the  rest  of  the  mixture 
without  the  application  of  external  heat. 

(2)  A  method  of  operating  the  process  described  in  claim  i, 
consisting  in  igniting  in  the  melting  vessel  a  small  quantity 
of  the  reduction  mixture  and  continuing  the  reaction  by  the 
addition  of  further  quantities  of  the  mixture,  which  may  finally 
be  added  in  the  briquetted  condition. 

(3)  A  method  of  operating  the  process  described  in  claim  i, 
characterized  by  heating  the  reaction  mixture  placed  in  the 
melting  crucible,  up  to  its  reaction  temperature  at  one  point 
only,  whereby  the  exothermic  reaction  propagates  itself  from 
this  point. 

(4)  In  the  method  of  partial  ignition  described  in  claims  i 
to  3  the  introductory  process  consisting  in  bringing  into  con- 
tact with  the  principal  mixture  and  igniting  another  mixture 
acting  upon  the  same  principle,  that  is,  consisting  of  alumin- 
ium  with  a  metallic  compound  (oxide  or  sulphide)  which  is 
easily  ignited  and  produces  a  high  reaction  temperature,1  and 
thus  communicates  the  ignition  to  the  principal  mixture. 

We  may  finally  draw  our  attention  to  the  fact  that  in  the 
patent  specifications  the  manufacture  of  manganese  is  given  as 
an  example,  while  this  metal  was  not  producible  according  to 
the  former  patent  (see  page  45),  evident!}'  in  consequence  of 

1  In    the  description    a  mixture  of  barium  peroxide   and   aluminium 
powder  is  given  as  an  example. 


BY  THE  USE  OF  HIGH  TEMPERATURES.  49 

the  extremely  high  temperatures  obtained  by  the  old  method 
of  operation. 

The  second  patent  already  referred  to,1  that  of  Vautin  an- 
nounced in  the  year  1896,  agrees  so  exactly  with  the  Gold- 
schmidt  patent  that  we  can  immediately  pass  to  its  patent 
claims,  which,  leaving  out  unnecessary  repetitions,  are  as  fol- 
lows: 

(i)  to  (8)  Process  for  the  production  of  metals  and  alloys 
from  metallic  oxides,  sulphides  or  chlorides  either  alone  or 
mixed  with  each  other,  by  the  reducing  action  of  aluminium, 
consisting  in  heating  to  the  reacting  temperature  a  small 
quantity  of  the  mixture  of  aluminium  or  aluminium-magnes- 
ium alloy  with  the  metallic  compounds,  the  latter  in  the 
finely  powdered  condition.  The  temperature  attained  by  the 
reaction  propagates  itself  successively  and  automatically  to 
the  adjacent  parts  of  the  mixture  and  ignites  the  whole  mass, 
as  above  described. 

(9)  The  process  described  for  the  production  of  metals  or 
alloys  from  metallic  oxides,  sulphides  or  chlorides  alone  or 
mixed  with  each  other,  characterized  by  heating  to  the  reac- 
tion temperature  a  small  quantity  of  the  mixture  of  the  finely 
pulverized  compound    and  finely  pulverized   aluminium    or 
aluminium-magnesium  alloy  in  order  to  start  the  reaction, 
and  then  adding  the  principal  part  of  the  mixture,  so  that  in 
consequence  of  the  heat  evolved  by  the  reaction  of  the  first 
part  the  main  reaction  is  propagated  automatically  through- 
out the  whole  mass,  as  before  described. 

(10)  The  process  described  for  the  reduction  of  metals  or 
alloys  from  metallic  oxides,  sulphides  or  chlorides  alone  or 
admixed  with  each  other,  characterized  by  covering  a  small 
portion  of  the  mixture  of  the  finely  pulverized  compound  with 
finely  pulverized  aluminium  or  aluminium-magnesium  alloy 
with  a  small  quantity  of  a  similar  mixture  which  is  more  easily 
started  in  action,  and  heating  the  latter  whereby  the  reaction 

1  English  Patent  16,685,  July  28,  1896. 


50  CHROMIUM  AND  ITS  COMPOUNDS. 

is  started  and  is  then  propagated   to  the  principal  mixture  as 
described. 

Finally  Dollner1  has  patented  the  use  of  carbides  in  place  of 
aluminiiim  or  magnesium.  "  The  details  of  the  process  aside 
from  the  replacement  of  aluminium  and  magnesium  by  the 
carbide  are  exactly  the  same  as  set  forth  in  the  above  patent 
specifications  Nos.  112,586  and  96,317."  The  reaction  tem- 
peratures are  somewhat  lower,  and  if  it  is  wished  to  raise  them 
aluminium  or  magnesium  may  be  mixed  in  ;  if  it  is  wished  to 
diminish  them  a  ballast  of  negative  material  can  be  added,  for 
instance,  an  excess  of  the  metallic  compound  to  be  reduced  or 
a  flux,  or  finally  an  excess  of  calcium  carbide  if  it  is  desired 
to  carbonize  the  metal  produced  or  to  introduce  calcium  into 
it. 

By  using  a  sufficient  excess  of  the  oxide  or  the  sulphide,  the 
metal  can  be  obtained  more  or  less  free  from  carbon,  at  least 
free  from  the  metallic  components  of  the  carbide.  It  is  not 
possible  to  produce  in  this  way  completely  carbonless  metals 
or  alloys,  and,  moreover,  the  evolution  of  gas  produced  by  the 
formation  of  carbon  monoxide  may  not  be  advantageous  to 
the  process. 

Patent  Claim. 

(1)  A  method  of  carrying  out  the  process  of  patent  No.  96,317, 
for  the  manufacture  of  metals  and  alloys  of  the  same  with 
each  other  or  with  metalloids,  using  a  mixture  of  oxygen  or 
sulphur  compounds  of  these  metals  or  metalloids  with  pulver- 
ized carbides  of  the  earth  or  alkaline  earth  metals,  with  or 
without   the   admixture   of   aluminium    or  magnesium,  and 
operating  the  process  in  such  a  manner  that  the  mixture  is 
ignited  at  one  point  and  thus  the  reaction  started  which  is 
concerned  in  the  production  of  those  metals  or  alloys. 

(2)  In  the  process  described  in  claim  i,  the  starting  of  the 
reaction  by  using  as  igniting  material  a  mixture  of  carbides 
and  oxides  in  composition   analogous  to  the  principal  mix- 

1  German  Patent  113,037,  Feb.  10,  1897. 


BY  THE  USE  OF  HIGH  TEMPERATURES.  51 

ture  but  reacting  more  violently,  and  thus  transferring  the 
ignition  to  the  principal  reacting  mass. 

(3)  A  method  of  operating  the  process  of  claim  i  for  the 
manufacture  of  alloys,  characterized  by  adding  the  compo- 
nents in  part  in  the  metallic  state  to  the  reacting-mixture  and 
not  in  reducing  both  of  the  components  of  the  alloy  simul. 
taneously  from  their  oxygen  or  sulphur  compounds.1 

Two  lectures  by  Dr.  Hans  Goldschmidt  given  in  iSgS2  and 
iQOi3  contain  some  further  additions  concerning  the  alumino- 
thermic  operations. 

It  is  stated  that  the  mixture  of  aluminium  with  the  oxide 
to  be  reduced,  called  thermite,  is  theoretically  made  in  quan- 
tivalent  proportions ;  though  in  general  an  excess  of  oxide  is 
used  since  it  is  thereby  possible  to  oxidize  completely  all  the 
aluminium  so  that  metal  free  from  aluminium  is  obtained,  in 
spite  of  the  great  alloying  tendency  of  aluminium. 

"  Before  all,  such  metals  are  to  be  considered  whose  produc- 
tion in  the  pure  state  has  not  been  possible  by  other  processes, 
or  even  in  the  electric  furnace  and  whose  production  now  in 
the  pure  carbonless  condition  would  offer  particular  advan- 
tages to  the  metallurgist.  Chromium  and  manganese  are  the 
most  important.  The  manufacture  of  these  metals  is  carried 
out  on  a  large  scale,  since  the  consumption  has  become  quite 
large  at  several  works. 

The  principal  consumption  is  supplied  by  the  Allgemeine 
Thermit-Gesellschaft  at  Bssen  ;  besides  them  the  French  So- 
ciete  d'filectro-Chimie  in  St.  Michael  de  Maurienne  (Savoy) 
has  manufactured  the  metals  named  in  particular  chromium, 
under  a  license  since  1899.  The  manufacture  is  carried  out 
in  large  crucible-shaped  vessels  in  which  several  hundred 
weight  of  the  metals  are  produced  in  one  operation ;  this 

1  Another  method  of  reduction  by  means  of  calcium  carbide  which  shows 
important  variations  from  the  above  has  so  far  been  only  incompletely  de- 
scribed.    See  Zeitschr.  f.  Elektrochemie,  7,  451  (1901). 

2  Zeitschr.  f.  Elektrochemie,  4,  494  (1898). 

3  Enlarged  reprint  from  Stahl  und  Eisen,  1901,  No.  n. 


52  CHROMIUM  AND  ITS  COMPOUNDS. 

operation  takes  scarcely  a  half  hour  in  consequence  of  the 
rapidity  of  the  reaction. 

On  top  of  the  metallic  mass  there  is  found  the  resulting 
alumina  which,  after  removal,  can  be  worked  up  again  into 
metallic  aluminium  in  the  most  suitable  manner.  The  metal 
reduced  from  it,  however,  contains  some  chromium  and  is 
therefore  best  used  again  for  the  manufacture  of  chromium, 
so  that  we  have  here  a  complete  cyclical  process  of  technical 
practicability. 

The  alumina  can  also  be  used  as  such,  since  it  is  quite  free 
from  water  and  therefore  possesses  many  advantages  over 
natural  emery  for  use  as  an  abrasive,  since  the  emery  on  ac- 
count of  its  small  water  content  does  not  possess  the  great 
hardness  of  the  corundum  made  by  fusion. 

The  slag  is  interesting  from  other  considerations.  It  shows 
small,  red,  transparent  crystals  mostly  in  small  cavities,  which 
are  to  be  regarded  as  true  rubies.  On  account  of  their  small- 
ness  they  do  not  possess  commercial  value. 

Concerning  the  pure  carbonless  chromium,  in  the  manu- 
facture of  which  pure  aluminium  must  be  used,  it  is  principally 
used  in  the  production  of  steel.  In  doing  so,  it  has  confirmed 
the  old  observation  that  metals  very  nearly  pure  possess  other 
qualities  than  those  contaminated  by  additions  and  that  by 
their  purity  the  properties  of  the  alloys  are  influenced  in  the 
foregoing  cases  quite  favorably. 

Some  further  communications  concerning  pure  chromium 
will  be  given  in  connection  with  the  chromium  alloys  at  the 
conclusion  of  the  next  section. 


II.    OBTAINING  OF  COMPOUNDS  OF  CHROM- 
IUM WITH  THE  METALS. 

A.  By  Electrolysis  of  Aqueous  Solutions. 

If  a  pure  solution  of  chromic  chloride  is  electrolyzed  with- 
out particular  precautions,  using  mercury  as  the  negative  and 
platinum  as  the  positive  electrodes,  the  mercury  according  to 
J.  Feree1  takes  up  only  traces  of  chromium,  and  there  results 
only  a  brownish  black  powder  whose  formula  according  to 
Bunsen  lies  between  Cr4O5  and  CrsO6  (see  however  later,  under 
chromium  oxides). 

In  order  to  obtain  large  quantities  of  chromium  amalgam  a 
solution  must  be  chosen  as  electrolyte  which  contains  160 
grams  of  crystallized  chromic  chloride,  100  grams  of  concen- 
trated hydrochloric  acid  and  740  grams  of  water,  and  the  cur- 
rent density  must  be  raised  somewhat  high.  With  a  current 
of  22  amperes  and  a  mercury  surface  of  8.05  sq.  cm.  that  is, 
a  current  density  of  2.73  amperes  per  square  centimeter  1.5 
kilograms  of  solid  chromium  amalgam  was  obtained  in  an 
hour.  A  too  feeble  current  density  is  to  be  avoided  since  with 
a  current  density  of  0.28  ampere  per  square  centimeter  the 
formation  of  amalgam  does  not  take  place. 

The  amalgam  formed  is  washed  quickly  with  cold  water 
after  pouring  off  the  solution,  and  is  then  pressed  out,  after 
being  dried  on  filter-paper,  in  a  piece  of  chamois  leather.  The 
mercury  pressed  through  the  leather  contains  only  traces  of 
chromium,  scarcely  0.03  per  cent.  The  amalgam  remaining 
in  the  leather  has  the  composition  Hg3Cr. 

If  this  amalgam  is  further  dried  by  laying  it  upon  double 
folded  filter-paper  and  subjecting  it  to  a  pressure  of  200  kilo- 
grams per  square  centimeter  for  several  minutes,  it  loses  more 
mercury  and  becomes  a  new  amalgam  having  the  formula 
HgCr. 

While  the  amalgam  Hg3Cr  is  soft,  lustrous,  only  slightly 
alterable  in  the  air,  loses  its  mercury  on  heating  without 
melting  and  easily  oxidizes,  the  amalgam  HgCr  is  also  lus- 

1  Compt.  rend.,  121,  822  (1895). 


54  CHROMIUM  AND  ITS  COMPOUNDS. 

trous  but  harder  and  more  easily  alterable  and  small  drops  of 
mercury  soon  form  on  its  surface.  Both  amalgams  leave  a 
residue  of  metallic  chromium  if  heated  in  a  vacuum  ;  the 
metal  is  very  crumbly,  but  retains  the  shape  of  the  original 
lump.  If  the  amalgam  is  distilled  in  a  vacuum  at  tempera- 
tures below  300°  it  leaves  (which  amalgam  is  not  stated)  a 
metallic  chromium,  the  qualities  of  which  are  very  different 
from  those  of  the  chromium  obtained  by  Deville  and  Fremy. 
This  chromium  is  pyrophoric  even  when  cold  ;  it  ignites 
spontaneously  in  the  air  and  absorbs  at  the  same  time,  in  a 
remarkable  manner,  both  nitrogen  and  oxygen.  The  heat 
generated  by  the  reaction  brings  the  whole  mass  to  a  bright 
incandescence.  The  chromium  produced  by  Moissan  by  the 
distillation  of  the  amalgam  below  350°  ignited  in  the  air  only 
when  it  was  warmed  slightly. 

The  pyrophoric  chromium  resembles  in  its  behavior  the 
pyrophoric  manganese  obtained  in  a  similar  manner  ;  even 
when  cold  it  absorbs  nitrogen  dioxide  with  incandescence, 
producing  chromic  oxide  and  chromic  nitride.  When  heated 
in  an  atmosphere  of  nitrogen  it  also  glows,  forming  chromic 
nitride.  Even  sulphur  dioxide  is  absorbed  in  the  cold  with 
incandescence,  and  a  slight  warming  in  an  atmosphere  of 
carbon  dioxide  or  carbonic  acid  will  suffice  to  set  the  chro- 
mium in  active  incandescence. 

After  heating,  the  pyrophoric  chromium  is  less  active  and 
almost  unchangeable  in  air. 

Some  further  communications  on  chromium  alloys  have 
already  been  given  on  pages  5,  10,  14,  15  and  23. 

B.  By  the  Use  of  High  Temperatures. 

Besides  the  processes  which  have  been  mentioned  in  de- 
scribing the  methods  for  producing  pure  chromium  (pages  zfl£,  3^ 
^et  seq\  there  are  some  others  which  are  recommended  for  the 
^manufacture  of  chromium  alloys  ;  according  to  Borchers1  there 
belongs  here  the  process  of  Moissan  patented  in 

1  Jahrbuch  der  Elektrochemie,  2,  183  (1895). 

2  German  Patent  82,624,  Nov.  9,  1894. 


BY   THE   USE   OF   HIGH   TEMPERATURES.  55 

Borchers  says:  "The  reason  why  chromium  and  similar 
metals  which  it  is  desired  to  obtain  free  from  carbon,  cannot 
be  manufactured  simply  by  processes  analogous  to  the  manu- 
facture of  aluminium  lies  in  their  high  melting-point.  Where 
the  presence  of  aluminium  is  not  injurious  the  manufacture 
of  the  more  easily  fusible  aluminium  alloys  of  these  metals  is 
recommended  after  the  general  idea  of  the  electrolysis  of 
alumina.  It  is  a  well-known  knack  of  alloying  to  take  one 
metal  which  is  not  fusible  easily  or  does  not  dissolve  quickly 
enough  in  a  second  metal  with  which  it  is  to  be  alloyed,  and 
to  dissolve  it  in  a  third,  which  forms  a  better  solvent  for  it,  in 
order  then  to  bring  it  in  a  dissolved  form  to  the  second  metal. 
This  process  has  been  patented  in  Germany  by  Moissan,  with 
his  usual  good  fortune  for  getting  patents  for  all  known 
things.  His  patent  concerns  the  difficultly  fusible  metals  and 
metalloids  such  as  molybdenum,  tungsten,  uranium,  zirconium, 
vanadium,  cobalt,  nickel,  manganese,  titanium,  chromium, 
silicon  and  boron  which  are  to  be  dissolved  in  iron  or  other 
metals.  He  gets  these  materials  at  first  in  solution  in  alumin- 
ium or  magnesium. 

In  fact  Moissan  does  not  say  that  his  process  is  to  be  operated 
electrolytically,  but  it  is  in  fact  operated  in  this  way  and  has 
been  done  so  several  years,  as  the  author  can  especially  verify. 
Those  metals  which  are  not  difficult  to  separate  out  electro- 
lytically, yet  are  hard  to  melt,  may  be  prepared  in  the  fluid  con- 
dition from  molten  electrolytes,  if  they  are  received  in  more 
easily  fusible  metals,  which  is  done  by  making  the  latter  the 
cathode  or  by  preparing  the  chromium  simultaneously  with 
the  other  metal." 

The  patent  specification  describes  the  bringing  the  alumin- 
ium or  magnesium  alloy  in  an  iron  bath,  or  other  suitable 
material  whereby  the  difficultly  fusible  elements  as  chromium, 
etc.,  are  taken  up  at  once  by  the  latter.  The  elimination  of 
the  aluminium  is  easy,  in  general  it  can  be  performed  by 
using  the  oxide  of  the  metal  with  which  one  is  working. 


56  CHROMIUM  AND  ITS  COMPOUNDS. 

"In  order  for  instance  to  get  chromium-copper  alloy  a 
determined  quantity  of  chromium-aluminium  is  added  to 
molten  copper,  according  to  the  content  of  chromium  which 
is  wished.  The  bath  is  well  stirred  and  if  the  quantity  of 
aluminium  present  is  too  high  and  must  be  removed,  the  ex- 
cess of  aluminium  is  burned  out  by  the  addition  of  small 
quantities  of  cupric  oxide,  and  the  aluminium  passes  into  the 
slag." 

In  other  cases  the  aluminium  in  excess  can  be  oxidized  uby 
the  gaseous  oxygen  present  in  the  solution,"  or  by  a  current 
of  air. 

An  alloy  of  iron  with  tungsten,  molybdenum,  and  chro- 
mium is  obtainable  in  the  Siemens-Martin  furnace  or  in  the 
Bessemer  converter  in  an  analogous  manner. 

Patent  Claim. 

Process  for  the  manufacture  of  alloys,  characterized  by  in- 
troducing the  difficultly  fusible  metals  molybdenum,  titanium, 
chromium,  etc.,  into  metals  and  alloys  in  the  form  of  alloys 
with  aluminium. 

A  process  for  the  commercial  manufacture  of  alloys  of  iron 
with  chromium,  etc.,  in  an  electrolytic  manner,  by  using  a 
flux  consisting  of  lime,  was  patented  by  J.  Heibling,  of 
Grenoble,  in  I895.1  He  uses  a  shaft  furnace,  the  inner  lining 
being  of  carbon  bricks  and  the  outer  of  refractory  bricks ;  a 
cast-iron  plate  lies  upon  the  movable  bottom  of  the  shaft, 
which  is  likewise  lined  with  carbon  bricks.  Above  the  latter, 
which  together  with  the  lining  of  the  furnace  acts  as  the 
negative  electrode,  is  the  positive  electrode  in  the  form  of  a 
carbon  rod  of  suitable  dimensions. 

A  carbon  crucible  is  made  "  by  placing  in  the  closed  cast- 
iron  form  a  suitable  mixture  of  pulverized  coke  or  graphite 
and  tar  and  baking." 

A  mixture  of  pulverized  ore  (oxide),  carbon  and  pulverized 
caustic  lime  is  brought  into  the  furnace,  the  lime  being  to  the 
carbon  in  the  proportion  of  3  molecules  to  i.  If  practicable 

1  German  Patent  86,503,  July  12,  1895. 


BY   THE   USE   OF   HIGH   TEMPERATURES.  57 

there  is  added  to  this  mixture  a  quantity  of  iron  oxide  neces- 
sary to  form  an  iron  alloy  of  a  certain  proportion,  with  the 
carbon  necessary  for  the  reduction,  in  which  case  the  weight 
of  the  cast-iron  furnace  bottom  is  to  be  taken  into  considera- 
tion. To  the  whole  mass  is  finally  added  a  suitable  quantity 
of  pulverized  fluor-spar  to  combine  with  the  silicon  in  excess. 

The  action  of  the  electric  current  is  described  as  follows : 
The  ore  and  finally  the  oxide  of  iron  is  reduced  and  forms  an 
iron  alloy  which  dissolves  the  carbon.  The  latter  unites, 
however,  immediately  to  form  calcium  carbide  with  the  cal- 
cium from  the  lime  (carbonic  oxide  being  formed).  The  car- 
bide contains,  dissolved,  the  remainder  of  the  silicon  as  carbide 
of  silicon  and  with  the  latter  forms  the  slag  under  which  the 
fluid  regulus  is  found.  By  inclining  the  movable  carbon 
bottom  to  one  side  the  alloy  can  be  drawn  off. 

The  silicious  material  serves  as  a  protection  for  the  calcium 
compound  which,  without  its  presence,  would  be  much  more 
easily  subject  to  attack  by  damp  air.  An  excess  of  silicon  is 
to  be  avoided. 

The  author  predicts  likewise  the  application  of  his  process 
in  particular  to  ores  poor  in  the  heavy  metals. 

The  patent  claim  reads :  Preparation  of  alloys  of  iron  with 
manganese,  chromium,  aluminium,  nickel  from  their  ores,  in 
the  electric  furnace,  characterized  by  the  use  of  lime  as  a  flux. 

In  contrast  to  the  processes  so  far  mentioned  which  work 
with  large  amounts  of  carbon  and  afterwards  treated  by  the 
process  of  Moissan  (see  page^g^,  furnishing  alloys  containing 
carbon,  stress  is  laid  by  La  Societe  Neo-Metallurgie  Marbeau, 
Chaplet  &  Co.,1  upon  the  obtaining  of  alloys  as  free  as  possible 
from  carbon.  For  this  purpose  they  also  use  a  "suitable 
electric  furnace"  which  is  apparently  lined  with  a  material 
containing  no  carbon,  and  heated  with  u  horizontal  arcs  in 
such  a  manner  that  contact  of  the  carbon  electrodes  with  the 
metal  and  oxides  in  question,  and  the  consequent  carburiza- 
tion  of  the  final  product  is  avoided." 

1  English  Patent,  7,847,  April  19,  1895. 


58  CHROMIUM  AND  ITS  COMPOUNDS. 

The  process  is  described  in  detail  as  follows  : 

A  sufficient  amount  of  a  more  or  less  easily  fusible  metal 
which  is  to  form  the  alloy  either  in  the  metallic  form  or  as  an 
oxide  mixed  with  the  necessary  amount  of  carbon  for  reduc- 
tion is  put  in  the  furnace,  heated  and,  after  reduction,  melted. 
To  the  bath  so  made  is  added  gradually  the  already  prepared 
oxide  of  the  heavy  metal  to  be  alloyed  mixed  with  the  req- 
uisite amount  of  carbon  for  reduction. 

Another  method  of  procedure  can  also  be  used  in  place  of 
the  one  already  mentioned :  "The  same  alloys  can  also  be  ob- 
tained by  mixing  the  oxide  of  the  difficultly  fusible  metal 
with  the  oxide  of  the  easily  fusible  metal  in  sufficient  quanti- 
ties and  in  the  right  proportions  to  form  the  desired  alloy. 

"  To  this  mixture  of  the  various  oxides  there  is  added  the 
proper  amount  of  carbon  for  reduction,  and  a  suitable  amount 
is  charged  into  the  furnace.  Under  the  influence  of  the  elec- 
tric arc,  the  oxide  of  the  more  easily  fusible  metal  is  first  re- 
duced and  melted  and  forms  the  foundation  of  the  metallic 
bath  by  which  is  gradually  accomplished  the  reduction  and 
fusion  of  the  other  oxide  (the  addition  of  the  mixture  of  the 
oxides  is  dependent  on  the  output  of  the  furnace)." 

Finally  there  can  be  added  to  the  bath  of  the  easily  fusible 
metal,  the  difficultly  fusible  metal  in  the  form  of  a  fine  powder, 
which  may  have  been  produced  by  an  electrolytic  process. 

The  composition  of  the  manufactured  alloy  can  be  easily 
calculated,  and  the  process  is  applicable  for  the  manufacture 
of  alloys  with  a  high  content  of  the  difficultly  fusible  metal 
(70  to  80  per  cent.)  which  then  in  this  condition  can  find  ap- 
plication as  additions  to  other  metals. 

It  is  quite  possible  with  this  process  to  obtain  alloys  quite 
low  in  carbon,  but  with  certainty  not  entirely  free  from 
carbon. 

The  patent  claim  reads : 

i.  The  preparation  of  improved  alloys,  as  described,  in  a 
suitable  furnace  heated  by  horizontal  arcs,  to  avoid  the  contact 


BY   THE    USE   OF   HIGH   TEMPERATURES.  59 

of  the  carbon  electrode  with  the  oxides  and  metals  in  question 
and  thereby  prevent  the  carburizing  of  the  finished  product, 
as  explained. 

2.  The  herein-described  improved  methods  for  the  prepara- 
tion of  improved  alloys  as  performed  in  various  cases  ;  as 
alloys  of  a  more  or  less  difficultly  fusible  metal,  as  chromium, 
tungsten,  molybdenum,  etc.,  with  a  more  easily  fusible  metal, 
as  nickel,   cobalt,  manganese,  iron,  copper,  aluminium,  etc., 
whereby  the  alloys  named  are  obtained  in  the  molten  metallic 
condition,  with  the  desired  content  of  each  the  single  con- 
stituents but  particularly  with  a  high  content  of  the  difficultly 
fusible  metal.     Such  alloys  are  more  easily  fusible  than  the 
more  difficultly  fusible  metal,  as  explained. 

3.  Various  applications  of  the  above-described  method  of 
preparing  alloys ;  in  particular  it  is  possible  to  add  a  diffi- 
cultly fusible  metal  when  molten  to  another  metal,   or  alloy, 
and  particularly  to  iron  and   steel  to  which  they  will   com- 
municate the  characteristics  of  the  difficultly  fusible  metal,  as 
explained. 

A  complete  exclusion  of  carbon  and  other  impurities  is 
possible  in  the  process  of  the  Electro-Metallurgical  Company, 
Limited,  of  London1,  for  the  preparation  of  chromium  alloys. 
In  the  description  the  effect  of  the  addition  of  chromium  will 
be  discussed,  although  it  is  pointed  out  that  the  chromium  is 
to  be  added  in  the  chemically  pure  condition,  in  particular  free 
from  carbon,  otherwise  the  property  of  the  alloy  will  be  in- 
juriously influenced. 

Further  it  is  remarked  that  the  addition  of  chemically  pure 
chromium,  electrolytically  prepared,  will  improve  all  metals  ; 
it  makes  them  harder  and  more  resistant  to  shocks,  tension, 
and  friction,  as  well  as  the  corrosive  action  of  air,  dampness, 
acids,  high  temperatures,  etc. 

Such  chromium  alloys  are  formed  only  when  the  chromium 
is  added  directly  to  the  molten  alloy.  Likewise  it  is  possible 

1  German  Patent  89,348,  IJan.  16,  1896  ;  English  Patent  of  Placet,  202, 
1896. 


60  CHROMIUM  AND  ITS  COMPOUNDS. 

to  add  one  or  more  metals,  which  facilitate  alloying  on  account 
of  their  large  capacity  for  dissolving  chromium,  as  zinc,  man- 
ganese, magnesium,  aluminium,  antimony,  bismuth,  palla- 
dium, etc.  Surely  this  last  can  only  find  application  on  paper. 

In  order  to  avoid,  in  this  process,  the  oxidation  of  the  chrom- 
ium, it  is  electrolytically  or  otherwise  covered  with  a  more 
or  less  thick  coat  of  a  protecting  metal,  as  copper,  nickel, 
gold,  silver,  zinc,  aluminium,  tin,  platinum. 

The  addition  of  chromium  in  very  small  amounts  exerts  a 
good  influence ;  a  few  tenths  of  a  per  cent,  makes  the  noble 
metals,  gold,  silver,  copper,  nickel,  tin,  as  well  as  lead  and 
zinc,  considerably  harder  and  tougher.  For  the  best  results 
the  chromium  should  be  added  in  the  proportion  of  0.5  up  to 
15  or  20  per  cent. 

The  metal  alloys  with  a  larger  content  of  chromium  are  so 
extraordinary  hard  that  they  can  only  be  worked  with  the 
grindstone.  Recapitulating,  the  great  advantages  of  the  addi- 
tion of  chromium  consist  as  follows  : 

An  addition  of  chromium  from  0.5  to  20  per  cent,  in  copper 
or  copper  alloys,  as  bronze,  brass,  German  silver,  etc.,  im- 
proves them  so  that  their  "fracture"  approaches  that  of  steel. 
A  small  addition  of  chromium  to  the  coinage  metals  makes 
them  noticeably  more  resistant  to  pressure  and  the  necessary 
washing.  Finally  chromium  makes  all  metals  as  well  as  al- 
loys more  resistant  against  high  temperatures,  and  is  valuable 
for  the  manufacture  of  hearth-plates  and  moulds,  also  more 
resistant  against  acids,  alkalies,  and  other  chemical  reagents, 
which  is  to  be  provided  against  in  the  manufacture  of  chem- 
ical apparatus  and  cooking  utensils ;  it  increases  the  hardness 
of  metals  and  their  ring,  as  of  bells  and  trumpets  ;  it  raises 
the  electric  resistance  of  manganese,  manganese-iron,  nickel- 
iron,  and  other  metals,  serving  for  the  manufacture  of  resis- 
tance wire;  and  raises  the  anti-magnetic  properties  of  copper, 
platinum,  palladium,  manganese,  tungsten,  and  cadmium,  a 
circumstance  made  use  of  in  the  construction  of  clocks,  etc. 

The  patent  claim  reads  : 


BY   THE   USE   OF   HIGH   TEMPERATURES.  6l 

Process  for  the  preparation  of  alloys  of  pure  chromium, 
characterized  by  the  fact  that  the  chromium  added  to  the 
bath  is  coated  previously  in  an  electrolytic  or  other  manner, 
with  a  coating  of  a  metal  (copper,  nickel,  aluminium,  gold, 
silver,  etc.),  which  prevents  the  oxidation  of  it  at  the  moment 
of  contact  with  the  bath. 

A  modification  of  this  process  of  the  same  company  is  de- 
scribed in  a  Russian  patent  of  September  13,  1897,  from 
which  the  Chemiker-Zeitung1  gives  an  extract.  According  to 
it  the  oxidation  of  the  chromium  will  be  prevented  by  being 
first  brought  into  contact  with  a  sufficient  amount  of  molten 
cryolite,  borax,  or  other  easily  fusible  flux  sufficient  to  cover 
it  and  then  the  metal  to  be  alloyed  added.  In  this  way  alu- 
minium will  readily  alloy  with  chromium,  although  otherwise 
even  on  long  heating  with  molten  aluminium  a  piece  of  chrom- 
ium will  not  dissolve  because  it  has  coated  itself  with  oxide. 

It  is  remarkable  that  at  these  high  temperatures  the  coating 
of  oxide  will  not  easily  be  reduced  by  aluminium,  although 
the  whole  process  of  Vautin-Goldschmidt  (see  page  ^efand 
following),  rests  on  this  fact ;  if  anything,  the  temperatures 
are  still  higher. 

The  process  can  also  be  worked  in  this  manner  :  Sufficient 
borax,  cryolite,  etc.,  can  be  added  to  form  a  complete  cover- 
ing to  the  molten  bath  and  then  pieces  of  the  hard  metal,  or 
it  may  be  the  alloy,  thrown  into  the  bath.  While  passing 
through  the  fluid  coating  the  metal  will  be  prevented  from 
oxidizing  and  any  coatings  of  oxide  will  be  dissolved  by  the 
flux.  To  avoid  contamination,  the  crucible  used  in  melting 
must  be  lined  with  alumina  or  chromic  oxide. 

For  completeness  we  have  an  American  patent2,  as  well 
as  that  of  the  Societe*  Generate  de  Aciers  Fins3,  both  patents 
concerning  the  manufacture  of  chromium-iron  alloys. 

1  Chemiker-Zeitg.,  p.  1068(1897). 

2  American    Patent   567,757,    Electrometallurgical    Company,    Limited, 
July  8,  1896  ;    the  Official  Gazette  of   the  U.  S.   Patent  Office,   76,    1642, 
1896,  nearly  corresponding  to  the  German  Patent  90,746,  of  the  I4th  of  June, 
1896. 

3  German  Patent  120,310,  April  6,  1899. 


62  CHROMIUM  AND  ITS  COMPOUNDS. 

The  first  patent  claim  reads  : 

The  described  improvements  in  the  treatment  of  iron  and 
steel  with  pure  chromium  or  similar  metals,  as  molybdenum 
or  tungsten,  for  the  preparation  of  alloys  of  these  metals,  con- 
sisting therein,  that  by  the  addition  of  a  proper  amount  of 
aluminium  to  the  molten  mass  of  iron  or  steel,  it  is  nearly 
completely  deoxidized,  the  deoxidation,  however,  by  the  alu- 
minium being  first  only  completed  after  a  small  part  of  the 
chromium  or  similar  metal  has  been  oxidized,  the  rest  alloy- 
ing with  the  mass  of  iron  or  steel. 

The  other  patent  claim  has  the  following  wording  : 

Process  for  the  manufacture  of  chrome-steel,  characterized 
by  allowing  a  stream  of  open-hearth  steel  to  flow  over  a  mix- 
ture of  aluminium  powder  and  chromium-iron  alloy  in  the 
casting  ladle. 

The  ignition  of  the  aluminium  by  the  outflowing  stream 
evolves  sufficient  heat  to  bring  the  surrounding  chromium- 
iron  alloy  to  a  quick  and  complete  fusion,  so  that  the  chrom- 
ium can  at  once  combine  intimately  with  the  stream  of  steel, 
and  the  cast-steel  block  which  is  characterized  by  great  den- 
sity and  freedom  from  blow-holes  also  shows  a  uniform  distri- 
bution of  chromium  throughout. 

In  concluding  the  processes  for  the  preparation  of  chromium 
alloys  the  process  of  Heroult1  for  the  preparation  of  very  rich 
ferro-chrome  must  be  considered.  In  the  reference  cited  it  is 
stated  that  chromite  is  heated  in  an  electric  furnace  with  the 
addition  of  a  sufficient  amount  of  carbon  for  reduction  and  38 
to  30  per  cent,  of  fluxing  material  (lime,  kaolin,  or  fluorspar). 
The  ferro-chrome  formed  will,  on  account  of  the  greater  vola- 
tility of  the  iron,  become  richer  in  chromium  the  quicker  the 
operation  is  completed  ;  the  fluxing  material  permits  the 
regulation  of  the  operation. 

Quite  identical  with  the  previous  patent  is  an  American 
patent2,  under  the  name  of  Vielhomme,  whose  claim  only 
was  accessible  to  me.  It  reads  : 

1  French  Patent  284,525,  Dec.  30,  1898  ;  Chemiker-Zeitg.,  694  (1899). 

2  U.  S.  Patent  648,119,   July  25,  1899;    the  Official  Gazette  of  the  U.  S. 
Patent  Office,  91,  717  (1900). 


BY   THE   USE   OF   HIGH   TEMPERATURES.  63 

Process  for  the  manufacture  of  rich  ferro-chrome,  consisting 
therein,  by  the  heating  of  chromite  in  an  electric  furnace  in 
the  presence  of  a  sufficient  amount  of  fluxing  material  and 
powdered  coke,  to  a  temperature  sufficient  for  reduction  and 
melting  of  the  ore  and  the  volatilization  of  the  larger  amount 
of  iron.  The  remaining  iron  then  forms  with  the  chromium 
a  rich  ferro-chrome  alloy.1 

At  this  place  also,  use  will  be  made  of  a  very  kind  letter  of 
Dr.  H.  Goldschmidt,  and  reference  made  also  to  page^&flmd 
the  literature  quoted  there,  and  some  general  remarks  on  the 
preparation  of  chromium  and  its  alloys  will  be  added. 

As  much  as  is  known  chromium  and  its  alloys  are  produced 
technically  in  four  ways  : 

i.  As  ferro-chrome  in  the  blast-furnace  ;  2,  as  ferro-chrome 
in  crucibles  ;  3,  as  ferro-chrome  in  the  electric  furnace  ;  4, 
as  pure  chromium  by  means  of  aluminium. 

The  blast-furnace  process  furnishes  no  particularly  rich 
chromium  product,  but  only  one  of  30  to  40  per  cent,  and 
may  get  into  a  difficult  position  because  at  this  day  higher 
percentage  alloys  are  preferred. 

Processes  2  and  3  furnish  alloys  containing  60  to  63  per 
cent,  of  chromium  and  8  to  12  per  cent,  of  carbon,  calculated 
on  the  chromium  content.  Large  quantities  are  produced  in 
this  way  in  France  and  Germany.  The  process  of  manufac- 
ture in  crucibles  in  which,  as  is  said,  only  a  single  kilogram 
can  be  made  at  one  time,  is  not  cheap.  The  composition  of 
the  chromium  mixtures  are  held  secret. 

Finally  this  process  has  been  somewhat  superseded  by  the 
electrical  process,  so  that  to-day  the  larger  amount  of  ferro- 
chrome  is  produced  in  the  electric  furnace,  and  particular 
preference  for  this  method  is  shown  in  France.  In  particular 
the  early  calcium  carbide  manufacturers,  who  had  to  give  up 

1  In  the  Russian  Privileg.,  351,  Sept.  30,  1897  (referred  to  in  Chemiker- 
Zeitg.,  1897,  1068),  E.  Placet  protects  a  process  for  the  manufacture  of 
chrome-iron  or  -steel,  Tubes  or  bars  on  which  chromium  has  been  electro- 
lytically  precipitated  were  melted  together  or  welded  or  drawn  into  wires  or 
cemented  ;  in  the  last  case  the  outer  surface  becomes  very  hard.  See  also 
page  ii. 


64  CHROMIUM  AND  ITS  COMPOUNDS. 

their  production  because  the  patents  of  Bullier  under  which 
they  worked  were  declared  legal  by  the  French  Court,  in 
opposition  to  the  German  Imperial  Court,  turned  to  this  new 
opportunity  with  avidity.  The  foundation  of  this  process  is 
indeed  that  given  by  Moissan  (page^j^T  35~ 

The  disadvantage  of  the  ferro-chromium,  particularly  that 
made  in  the  electric  furnace,  which  probably  contains  a  few 
more  per  cent,  of  chromium  than  that  made  in  the  crucible, 
lies  in  its  high  and  irregular  content  of  carbon,  so  that  for  the 
best  qualities  of  steel  alloys,  especially  if  several  per  cent,  of 
chromium  is  to  be  added,  it  cannot  always  be  used. 

For  instance  if  it  is  a  question  of  increasing  the  content  of 
chromium  relatively  to  the  carbon  which  is  added  to  Martin 
steel  in  the  prepared  condition  at  the  end  of  the  operation  so 
as  to  provide  a  charge,  for  instance,  which  along  with  2.5  per 
cent,  of  chromium  shall  contain  0.2  or  scarcely  only  0.15  per 
cent,  of  carbon,  this  cannot  be  obtained  without  the  assistance 
of  carbon-free  chromium  ;  since  when  using  ferro-chromium  at 
least  0.25  to  0.3  per  cent,  of  carbon  is  carried  in,  which  with 
the  carbon  already  in  the  fluid  metal  raises  the  percentage  to 
at  least  0.3  or  0.35  per  cent,  in  the  finished  metal.  Also  in 
crucible  casting  even  where  small  additions  of  chromium  are 
concerned,  i  to  2  per  cent.,  and  where  therefore  a  particularly 
small  carbon  content  of  the  alloy  added  is  not  of  importance, 
carbon-free  chromium  is  preferred. 

Further,  carbon-free  chromium  is  used  for  the  manufacture 
of  high  chromium  tool  steel  containing  6  to  10  per  cent,  or 
even  more  chromium. 

It  is  worth  mentioning  that  the  addition  can  be  made  in  the 
form  of  chrome-thermite  (as  the  mixture  of  aluminium  and 
chromium  oxide  is  called).  It  is  used  in  the  manner  that  the 
highly  heated  steel  is  allowed  to  flow  upon  the  mixture  men- 
tioned and  immediately  ignites  it.  The  chromium  dissolves 
in  the  metal  bath,  while  the  slag  floats  on  the  top  (see  page 

56). 


BY  THE  USE  OF  HIGH  TEMPERATURES.  65 

On  the  grounds  before  mentioned,  in  spite  of  the  fact  that 
the  ferro-chromium  prepared  in  the  electric  furnace  is  much 
cheaper,  pure  chromium  prepared  from  chromium-thermite  is 
often  preferred.  The  last  ignites  itself  only  at  very  high  tem- 
peratures as  has  been  stated,  and  yields  a  good  output  only 
when  used  in  large  amounts. 

The  market  price  of  60  per  cent,  ferro-chrome,  according  to 
the  quotations  of  December  15,  1901,  was  $350  per  metric 
ton  ;  it  may  upon  large  demands  become  much  lower.  It  was 
much  higher  a  short  time  ago  before  the  introduction  of  the 
electrical  process. 

The  price  of  commercially  pure  chromium  is  $2  per  kilo. 
In  spite  of  that  the  product  is  used  by  many  firms  by  the  car- 
load. 

Besides  ferro-chromium  there  is  still  another  rich  chromium 
alloy  which  finds  many  applications,  the  chrome-manganese 
containing  70  per  cent,  of  manganese  and  30  per  cent,  of 
chromium.  It  is  used  in  the  manufacture  of  copper  alloys, 
the  so-called  chrome-manganin.  Chromium  alloys  directly 
with  copper  with  great  difficulty,  it  liquating  out  quite  easily 
so  that  the  chromium-copper  with  10  per  cent,  of  chromium 
made  by  the  alumino-thermite  process  and  used  in  the  manu- 
facture of  chromium-treated  copper  is  very  seldom  chosen, 
while  the  chrome-manganese  alloys  easily  with  copper  like 
pure  manganese  itself  and  has  just  recently  come  into  frequent 
use. 

In  contrast  to  iron,  chromium  seems  to  raise  the  ductility  of 
copper.  A  chrome-copper  with  10  per  cent,  of  chromium  has 
almost  completely  the  color  of  pure  copper,  but  is,  however, 
considerably  harder. 


III.     OBTAINING    OF    THE    COMPOUNDS    OF 

CHROMIUM  WITH  THE  NON-METALS. 

A.  Carbon  Compounds. 

It  has  often  been  stated  in  the  description  of  the  methods 
serving  for  the  manufacture  of  chromium,  that  the  chromium 
often  contains  carbon.  We  shall  now  give  information  re- 
garding the  obtaining  of  well-characterized  compounds  of 
chromium  with  carbon,  which  has  appeared  in  the  work  of 
Moissan1  already  referred  to  (see  page  3$,  et  seq.\ 

If  a  crucible  containing  chromium  and  a  large  excess  of 
carbon  be  heated  in  an  electric  furnace  using  350  amperes  at 
70  volts  for  from  ten  to  fifteen  minutes,  there  is  obtained  an  inco- 
herent mass  in  the  bottom  of  the  crucible  filled  with  crystals 
of  chromium  carbide  of  the  formula  C2Cr  (according  to  two 
analyses).  This  carbide  forms  in  lamellae  of  very  high, 
somewhat  greasy  lustre,  and  is  only  slowly  attacked  by  dilute 
hydrochloric  acid  on  long  standing,  not  by  concentrated  hy- 
drochloric acid,  fuming  or  dilute  nitric  acid,  or  aqua  regia. 
It  is  slightly  attacked  by  molten  caustic  potash,  but  on  the 
contrary  molten  saltpeter  attacks  it  with  ease.  Its  specific 
gravity  is  5.62.  Hot  water  is  not  decomposed  by  it. 

The  formation  of  another  carbide  has  been  observed  in  a 
number  of  preparations  of  metallic  chromium.  The  surface 
of  the  metallic  pieces  are  seen  to  be  covered  with  brownish 
red  needles,  which  often  reach  a  length  of  i  to  2  cm,  and  show 
the  composition  CCr4  (after  three  analyses).  Sometimes  this 
carbide  takes  the  form  of  shining  needles  lining  the  cavities 
which  form  in  the  molten  chromium.  Its  density  is  6.75. 

Both  compounds  dissolve,  on  a  further  raising  of  the  tem- 
perature, large  quantities  of  carbon,  which  they  then  again  give 
up  in  the  form  of  small  shining  folia  of  well  crystallized 
graphite. 

P.  Williams2  obtained  a  double  carbide  of  iron  and  chrom- 
ium, on  heating  a  mixture  of  200  grams  of  pure  calcined 
chromic  oxide,  200  grams  of  iron  and  70  grams  of  petroleum 
coke  in  a  carbon  crucible  for  five  minutes,  using  900  amperes 

1  Compt.  rend.,  119,  185  (1894). 

2  Ibid.,  127,483(1898). 


SILICON    COMPOUNDS.  67 

and  45  volts.  The  resulting  metallic  mass  had  a  crystalline 
appearance  and  resembled  commercial  ferro-chromium.  On 
treating  from  two  to  three  hours  on  the  water-bath  with  aqua 
regia  it  was  gradually  disintegrated,  and  the  crystals  which  sepa- 
rated were  retreated  anew  to  separate  from  them  the  last  traces 
of  iron.  They  were  separated  from  the  remaining  impurity, 
a  small  amount  of  graphite,  by  means  of  bromoform. 

The  crystals  had  a  metallic  appearance,  somewhat  the  color 
of  nickel,  and  consisted  of  a  conglomeration  of  tough  needles; 
they  scratched  glass  but  not  quartz,  were  not  magnetic  and 
had  a  density  of  7.22  at  19°.  They  oxidized  at  about  500° 
in  a  stream  of  air  or  steam.  Gaseous  or  liquid  acids  attack 
them  slowly,  nitric  acid  and  aqua  regia  being  without  appre- 
ciable effect.  The  analysis  gave  the  composition  of  3Fe3C. 
2CrsC2.  It  was  also  noticed  that  an  excess  of  iron  carbide 
easily  changed  the  results  of  analysis. 

B.  Silicon  Compounds. 

In  connection  with  the  description  of  the  manufacture  of 
the  hardest  possible  materials,  which  will  scratch  chromium 
steel,  the  ruby  and  even  the  diamond,  such  as  the  silicide  and 
boride  of  titanium,  carbon,  etc.;  it  was  mentioned  by  F.  Chap- 
let1  that  in  the  same  manner  also  the  silicides  of  the  metals, 
zirconium,  chromium,  iron,  nickel,  cobalt,  manganese,  molyb- 
denum, tungsten,  uranium  and  vanadium  may  be  pre- 
pared containing  various  amounts  of  nitrogen  and  carbon. 
This  patent  demands  more  attention  on  this  account. 

For  preparing  the  silicide  of  titanium,  for  instance,  the  fol- 
lowing process  was  proposed  :  82  parts  of  pulverized  rutile, 
60  parts  of  sand  and  48  parts  of  pulverized  carbon  are  mixed 
together.  The  dry  mixture  is  pressed  into  a  carbon  crucible, 
placed  in  an  electric  furnace,  built  somewhat  like  Moissan's 
with  movable  electrodes,  which  is  closed  up  and  heated  for  a 
longer  or  shorter  time  according  to  the  strength  of  the  current. 

There  is  obtained  a  gray,  fused  mass  which,  after  cooling,  has 
a  shiny  fracture,  is  of  great  hardness  and  has  a  density  of 
about  4.8  and  which  can  contain  according  to  the  duration  of 

1  English  Patent  15,453,  August  14,  1893. 


68  CHROMIUM  AND  ITS  COMPOUNDS. 

heating,  besides  the  titanium  and  silicon,  20  to  25  per  cent, 
of  carbon  and  a  varying  amount  of  nitrogen.  This  compound 
•can  also  be  obtained  in  a  crystalline  state  if  a  metal  in  the 
molten  state  is  employed  as  a  solvent  and  is  afterwards  re- 
moved by  a  suitable  acid. 

For  further  particulars  of  the  process  a  reproduction  of  the 
detailed  patent  claim  will  suffice : 

(1)  The  manufacture  or  production  of  hard  materials,  which 
are  able  to  scratch  chrome  steel,  and  scratch  or  cut  rubies  or 
diamonds,  characterized  by  subjecting  a  mixture  of  the  neces- 
sary materials  with  or  without  reducing  agents,  as  desired,  in 
a  crucible  to  the  heat  of  the  electric  arc,  whereby  there  is  ob- 
tained the  desired  substances  in  pure  crystallized,  amorphous 
or  melted  condition,  or  in  the  last  case  dissolved  in  a  suitable 
metal  as  solution  medium  from  which  it  crystallizes  out,  and 
then  after  the  solution  of  the  metal  in  an  acid  can  be  obtained 
in  the  form  of  hard  crystals. 

The  process  can  be  carried  out  as  follows:  i.  By  a  simple 
direct  combination  of  the  mixed  materials ;  2.  By  the  direct 
combination  of  the  mixed  materials  in  the  presence  of  an  excess 
of  a  metal  which  can  be  later  removed  by  the  aid  of  an  acid ; 
3.  By  preparation  of  the  material  from  an  oxide  or  a  salt  of 
one  of  its  constituents,  by  reduction  and  solution  in  a  metal 
from  which  it  can  be  afterwards  obtained  by  removal  of  the 
metal  essentially  as  carried  out  above. 

(2)  The  various  new  hard  compounds  which  have  been  pre- 
pared  by  the  above  process,  as  the  silicide  and    boride    of 
titanium,  as  well  as  other  silicides  and  borides,  the  silico- 
carbide  and  silico-boride  of  titanium,  and  the  silicides,  boro- 
silicides  and  silico-carbides  of  other  metals  and  metalloids,  are 
able  to  scratch  chromium  steel  and  to  scratch  or  cut  rubies  or 
diamonds,  and  in  the  pulverized  form  as  abrasive  material, 
glued  to  paper  or  cloth,  for  cutting,  polishing  or  grinding. 

Moissan1  gives  more  exact  information  regarding  the  com- 
mercial methods  used  in  the  preparation  of  chromium  silicide. 
After  mentioning  briefly  that  chromium  and  silicon  will  com- 
1  Compt.  rend.,  121,  624  (1895). 


SILICON   COMPOUNDS.  69 

bine  in  a  reverberatory  furnace  in  a  current  of  hydrogen  at  a 
temperature  of  1200°,  he  turned  his  investigations  to  the  elec- 
tric furnace. 

If  100  parts  of  chromium,  free  from  carbon,  and  15  parts  of 
silicon  are  brought  together  in  a  carbon  crucible,  and  subjected 
to  a  current  of  900  amperes  at  50  volts  for  nine  minutes,  there 
will  be  found  a  silicide  with  a  crystalline  fracture  embedded 
in  the  surplus  metal. 

Or  if  60  parts  of  silica,  200  parts  of  chromium  oxide  and 
70  parts  of  sugar  carbon  be  heated  together  with  a  current  of 
950  amperes  at  70  volts  for  ten  minutes,  there  is  found  a  well- 
fused,  brittle  and  crystalline  metallic  mass.  In  the  interior  are 
found  spaces  filled  with  needles  of  chromium  silicide.  This 
metallic  mass  is  coarsely  pulverized  and  treated  for  a  short 
time  with  cold  concentrated  hydrofluoric  acid,  until  the  acid 
attacks  actively,  then  moderating  the  action  by  the  addition 
of  water,  in  order  to  avoid  raising  of  the  temperature  and  de- 
composition of  the  silicide.  It  must  now  be  washed  alternately 
with  water  and  cold  hydrofluoric  acid  until  all  action  has 
ceased  ;  the  residue  consists  of  single  or  coherent  small  prisms 
of  silicide,  which  often  are  contaminated  by  small  amounts  of 
silicon  carbide. 

The  chemical  properties  of  the  chromium  silicide  remind 
one  of  iron  silicide,  especially  in  its  behavior  towards  acids ; 
if  finely  pulverized  it  is  attacked  by  hot  strong  hydrochloric 
acid.  Nitric  acid  has  but  slight  effect,  while  aqua  regia  de- 
composes it  with  the  formation  of  silica.  The  gaseous  hy- 
drogen acids  attack  it  only  at  temperatures  lying  between 
dark  and  bright  red  heats.  At  700°  gaseous  hydrochloric 
acid  transposes  both  the  chromium  and  silicon  into  chlorine 
compounds. 

Chlorine  alone  acts  at  a  red  heat  causing  the  silicide  to 
glow  brightly.  Molten  potassium  nitrate  quickly  forms  chrom- 
ate  and  silicate,  while  caustic  potash  acts  only  slowly. 

The  silicide  scratches  quartz  and  even  corundum  with 
greatest  ease;  it  appears  that  the  majority  of  the  silicides 


70  CHROMIUM  AND  ITS  COMPOUNDS. 

possess  a  much  greater  hardness  than  the  corresponding  car- 
bides. 

For  performing  the  difficult  analysis  the  silicide  is  fused 
with  a  mixture  of  2  parts  of  potassium  carbonate  and  8 
parts  of  potassium  nitrate,  and  afterwards  treated  with  hydro- 
chloric acid.  The  separation  of  the  silica,  which  was  made 
insoluble  by  two  treatments  on  the  sand-bath,  was  tedious. 
The  presence  of  carbo-silicides  complicated  the  analysis.  The 
results  found  corresponded  closely  to  the  formula  SiCr2. 

SiCr2. 

Chromium 80.22         79.83        80.36        78.79 

Silicon 19.60        21.08         19.92         21.21 

Another  much  softer,  but  with  the  exception  of  hydrofluoric 
acid  also  resistant  to  acids,  crystallized  chromium  silicide  of 
the  formula  SiCrs  was  prepared  by  Zettel1  by  heating  in  a 
Perrot  furnace  and  utilizing  the  heat  set  free  by  the  reduction 
of  chromium  oxide  by  aluminium,  in  which  he  melted  140 
grams  of  copper  and  140  grams  of  aluminium  in  a  refractory 
crucible  and  gradually  added  200  grams  of  previously  ignited 
chromic  oxide.  The  mixture  was  vigorously  stirred,  and  to- 
wards the  end  some  aluminium  filings  were  added  ;  the  silicon 
came  from  the  crucible  and  from  the  stirrer  of  like  material. 

In  experiments  to  produce  these  silicides  in  the  electric  fur- 
nace, mixtures  of  many  chromium  silicides  were  obtained  but 
could  not  be  separated  from  each  other  because  of  their  similar 
chemical  behavior. 

Moissan  and  Zettel  in  their  investigations  used  chromium 
in  excess  and  likewise  obtained  compounds  containing  chrom- 
ium in  excess.  De  Chalmot2  carried  on  his  researches  in 
quite  a  different  direction ;  he  heated  chromium  oxide  with 
wood  charcoal  and  an  excess  of  silica  in  the  electric  arc,  and 
obtained  large  needles  of  a  gray  color  and  brilliant  metallic 
lustre,  which  were  embedded  in  free  silicon  and  could  only  be 
separated  from  it  mechanically  with  difficulty.  Cold  hydro- 

1  Compt.  rend.,  126,  833. 

'2  Am.  Chem.- Journal,  19,  69  (1897). 


PHOSPHORUS    COMPOUNDS.  7 1 

chloric  acid  and  aqua  regia  had  no  effect  on  it,  hydrofluoric 
acid  dissolved  it,  which  fact  was  made  use  of  for  separating  out 
free  silicon.  Two  analyses  showed  a  composition  correspond- 
ing to  the  formula  Si2Cr,  in  one  of  which  was  found  13. 84  per 
cent,  of  free  silicon  and  in  the  other  4.71  per  cent.;  the  last 
one  had  a  density  of  4.393.  The  chromium  silicide  is  charac- 
terized by  great  tendency  to  crystallize  even  in  the  presence 
of  much  free  silicon. 

In  a  later  publication1  the  same  author  makes  a  statement 
regarding  the  behavior  of  the  above-described  chromium-sili- 
cide  towards  sulphur.  Under  300°  almost  no  reaction  took 
place,  while  at  a  higher  temperature  some  silicon  disulphide 
and  not  free  silicon  (as  with  copper  silicide,  Cu2Si)  could  be 
detected.  The  affinity  of  chromium  for  silicon  is  therefore 
under  these  conditions  somewhat  greater  than  that  of  copper. 

C.  Phosphorus  Compounds. 

Th.  Parker  made  the  observation  that  in  the  electrolysis  of 
chloride  solutions,  if  chromium  phosphide  is  used  as  anode,  it 
was  in  general  not  seriously  attacked  by  the  chlorine  set  free, 
and  in  1892*  protected  the  application  of  chromium  phosphide 
as  anode  material  in  the  following  patent  claim : 

An  anode,  in  cells  for  the  electrolysis  of  solutions  contain- 
ing chlorides,  consisting  of  or  containing  chromium  phos- 
phide, essentially  as  previously  described. 

The  patent  literature  gives  several  details  regarding  the 
preparation  of  the  chromium  phosphide  ;  chromium  phosphate 
is  mixed  with  carbon  and  if  necessary  a  fluxing  material,  and 
decomposed  in  any  furnace  at  a  high  temperature,  whereby 
chromium  phosphide  is  formed.  Or  chromium  phosphate  or 
chromium  oxide  and  other  phosphates  like  calcium  or  alumin- 
ium phosphate  can  be  heated  to  the  necessary  temperature 
in  an  electric  furnace. 

The  chromium  phosphate  used  as  crude  material  need 
in  no  way  be  pure. 

1  Amer.  Chem.  Journal,  19,  871  (1897). 

2  English  Patent  6,007,  March  28,  1892. 


72  CHROMIUM  AND  ITS  COMPOUNDS. 

Should  the  chromium  phosphide  anode  be  attacked  at  very 
high  current  densities,  the  chromium  which  has  gone  into- 
solution  can  be  very  easily  removed. 

Another  process  for  the  preparation  of  chromium  phosphide 
has  been  proposed  by  S.  Maronneau1.  He  had  found  that  by 
the  reduction  of  copper  phosphate  with  carbon  in  the  electric 
furnace  a  copper  phosphide  could  be  obtained,  which  was- 
stable  at  the  temperature  of  boiling  copper.  This  led  him  to 
believe  that  by  the  help  of  copper  phosphide,  the  phosphides 
of  the  other  metals  and  also  that  of  chromium  could  be  pro- 
duced. He  used  for  this  purpose  a  commercial  copper  phos- 
phide containing  90  per  cent,  of  copper  and  10  per  cent,  of 
phosphorus.  He  mixed  100  parts  of  this  copper  compound 
with  10  parts  of  chromium  filings,  which  had  been  made  by 
the  process  of  Moissan.  After  four  minutes  heating  with  a 
current  of  900  amperes  at  45  volts,  he  found  a  somewhat 
crumbly  metallic  material  with  a  crystalline  structure  from 
which  could  be  isolated,  by  the  use  of  concentrated  nitric 
acid,  a  chromium  phosphide  of  the  formula  CrP.  It  occurs 
as  dull  gray  crystals,  is  insoluble  in  all  acids  with  the  excep- 
tion of  a  mixture  of  nitric  and  hydrofluoric  acids,  and  at  15°" 
has  a  density  of  5.71. 

D.  Sulphur  Compounds. 

Mourlot2  also  used  the  electric  furnace  in  his  investigations 
on  the  production  of  the  sulphur  compounds  of  chromium.  He 
first  heated  100  grams  of  metallic  chromium  for  from  six  to 
eight  hours  in  a  reverberatory  furnace  heated  by  coke,  leading 
dry  hydrogen  sulphide  over  it.  The  metallic  mass  so  ob- 
tained showed  a  crystalline  fracture,  could  be  easily  ground  to 
a  black  powder,  and  from  appearances  corresponded  to  the 
protosulphide  CrS.  If  heated  three  to  four  minutes  in  an  elec- 
tric furnace  with  a  current  of  900  amperes  at  50  volts,  it  melted 
completely  and  on  cooling  formed  a  regulus  with  a  beautiful 
crystalline  fracture,  and  with  cavities  containing  prismatic 

1  Compt.  rend.,  ISO,  656  (1900). 
*  Ibid.,  121,  943(1895). 


OXYGEN    COMPOUNDS.  73 

needles.  Long  heating  in  contact  with  carbon  causes  decom- 
position. This  crystalline  sulphide  has  a  density  of  4.08,  and 
scratches  quartz  somewhat  easily.  Fluorine  attacks  it  strongly 
at  a  low  red  heat ;  chlorine  at  340°  with  the  formation  of 
chromic  chloride  and  sulphurous  chloride.  Bromine  reacts 
only  at  higher  temperatures,  and  iodine  not  at  all. 

Oxygen  acts  violently  at  a  low  red  heat  with  the  formation 
of  chromic  oxide  and  sulphur  dioxide,  assuredly  also  SCK 
Also  gaseous  hydrochloric  and  hydrofluoric  acids  act  on  it, 
the  latter  even  at  low  temperatures.  Sulphuric  acid  reacts 
only  when  heated  ;  there  results  sulphur,  sulphurous  acid  and 
chromic  sulphate.  Nitric  acid  and  aqua  regia  decompose  the 
chromium  sulphide  at  ordinary  temperatures.  Hydrogen  sul- 
phide is  evolved  by  the  action  of  steam  at  a  red  heat,  and  non- 
crystallized  chromic  oxide  remains  behind.  It  is  easily 
oxidized  by  energetic  oxidizing  agents,  also  by  molten  potash. 
Reducing  materials  react  only  with  difficulty  ;  hydrogen  not 
even  at  1200°.  On  heating  with  carbon  in  the  electric  fur- 
nace there  is  obtained  according  to  the  time  more  or  less 
molten  metallic  chromium  containing  more  or  less  sulphur. 

E.  Oxygen  Compounds. 

(1)  Chromous  Oxide  Compounds. 

The  chromous  oxide  compounds  have  up  to  recently  not 
been  easily  obtainable  and  at  no  time  have  played  any  im- 
portant part  in  chemical  technology.  They  are  important 
because  of  the  great  power  of  reduction  they  possess,  so 
it  would  appear  desirable  to  discover  a  convenient  method  of 
preparation  in  order,  if  opportunity  offered,  to  be  able  to  make 
use  of  them  in  technical  processes. 

From  an  American  patent  of  Villon1,  from  which  we  extract 
the  following  from  the  patent  claim,  it  is  seen  that  active 
search  is  being  made  to  make  practical  this  method  of  reduc- 
tion, but  chromium  is  too  expensive  after  utilizing  its  power 
of  reduction  for  the  proposed  purpose,  to  throw  aside  the  use- 

1  Gazette  U.  S.  Patent  Office,  84,  846  (1898)  ;  U.  S.   Patent  608,652, 
March  n,  1897. 


74  CHROMIUM  AND  ITS  COMPOUNDS. 

less  chromic  salt,  so  it  is  desired  at  the  same  time  to  make 
the  chromium,  by  the  help  of  the  electric  current,  a  means  of 
continuously  transferring  hydrogen.  The  chromic  oxide  salt 
formed  by  the  process  of  reduction  should  be  reduced  back  in 
a  simple  manner  at  the  cathode.  The  heretofore-mentioned 
extract  of  the  patent  claim  which  is  concerned  with  the  manu- 
facture of  ethyl  alcohol  reads  : 

"  The  herein-described  process  for  the  manufacture  of  ethyl 
alcohol,  consisting  in  the  decomposition  of  calcium  carbide  by 
water,  by  which  acetylene  is  formed,  and  in  the  treatment  of 
the  acetylene  by  chromium-ammonium  double  sulphate,  thus 
producing  ethylene,  in  the  absorption  of  the  ethylene  .  . 
and  finally  subjecting  the  reducing  agent  to  the  action  of  the 
electric  current  either  unbrokenly  or  in  subdivided  spaces. " 
I  have  found  no  further  information. 

The  preparation  of  chromous  oxide  salts  in  the  solid  form 
has  been  protected  within  a  few  years  by  Boehringer  and 
Sons.1  According  to  the  patent  specifications  the  process  is 
carried  out  in  the  following  manner :  The  anode  space  of  a  de- 
composition cell,  provided  with  a  diaphragm,  is  filled  with  a 
30  per  cent,  sulphuric  acid  solution.  In  the  cathode  space  is 
poured  a  mixture  of  500  parts  by  weight  of  chromium  sul- 
phate in  500  parts  by  volume  of  water  and  250  parts  by 
volume  of  Concentrated  sulphuric  acid.  This  is  reduced  by 
the  use  of  lead  for  electrodes  and  a  high  current  density  of 
1000  to  1500  amperes  per  square  metre  =  from  o.  10  to  o.  1 5  am- 
pere per  square  centimetre. 

The  chromous  sulphate  falls  as  a  bluish-green,  fine-grained 
crystalline  powder,  which  can  be  separated  from  the  adhering 
mother-liquor  by  filtration  and  washing  with  alcohol.  It 
contains  one  molecule  of  water  of  crystallization,  does  not 
change  in  the  air,  and  appears  to  be  identical  with  the  recog- 
nized salt2  CrSO4.H2O  which  is  obtained  by  treating  CrSCK 
7H2O  with  concentrated  sulphuric  acid  and  which  also  changes 
but  little  in  the  air. 

1  German  Patent  115,463,  May  5,  1899. 
*  Dammer,  Anorgan.  Chemie,  3,  546. 


OXYGEN    COMPOUNDS.  75 

It  dissolves  slowly  in  water  to  a  pale  bluish-green  solution. 

If  in  place  of  chromic  sulphate  and  sulphuric  acid,  chromic 
•chloride  and  hydrochloric  acid  is  used  as  cathode-electrolyte, 
and  treated  as  before,  chromous  chloride  is  obtained  as  a 
green,  granular  crystalline  mass. 

The  patent  claim  reads  : 

Process  for  the  preparation  by  electrolysis  of  chromous 
•oxide  salts  in  the  solid  form  from  chromic  oxide  salts,  charac- 
terized by  subjecting  concentrated  acid  chromic  oxide  salt  so- 
lutions in  the  cathode  compartment  of  an  electrolytic  cell  to 
the  electric  current. 

In  an  experiment,  to  prepare  chromous  sulphate  according 
to  the  directions  given  in  the  patent  claim,  Dr.  F.  Glaser  ob- 
tained the  following  results  in  my  laboratory:  On  electrolyz- 
ing  a  cathode  solution  consisting  of  200  grams  of  Cra(SO4)3 
(calculated  on  anhydrous  salt),  200  cc.  of  water  and  100  cc.  of 
concentrated  H2SO4,  for  some  time,  with  a  current  density  of 
o.  10  to  0.15  ampere  per  square  centimetre,  there  separated  out 
solid  chromous  sulphate  in  bluish-green,  thread-like  crystals. 
They  were  quickly  filtered  and  the  adhering  mother-liquor 
washed  from  them  with  a  small  amount  of  sulphuric  acid 
(i  :  i)  and  then  washed  with  alcohol  and  dried  between  filter- 
paper.  If  the  mother-liquor  in  the  cathode  space  was  electro- 
lyzed  still  further,  only  a  very  small  amount  of  fresh  chromous 
salt  was  formed,  although  the  remaining  solution  was  still 
quite  rich  in  chromic  salt.  It  appeared  meanwhile  as  if  the 
migrating  SO  ions  increased  the  solubility  of  the  chromous 
sulphate ;  the  addition  of  concentrated  sulphuric  acid  removed 
the  difficulty.  For  the  further  continuance  of  the  process, 
fresh  chromic  oxide  salt  was  added  from  time  to  time. 

The  chromous  salt  was  not  obtained  pure  at  any  time,  but 
always  mixed  with  the  chromic  salt,  since  it  is  very  easily 
oxidized,  and  at  ordinary  temperatures  slowly  decomposes 
water  with  an  evolution  of  hydrogen.  Also  during  the  filtra- 
tion and  sucking  dry  a  continual  oxidation  took  place,  raising 
the  temperature  somewhat  high.  In  consequence  the  output 
was  disappointing. 


76  CHROMIUM  AND  ITS  COMPOUNDS. 

In  contrast  to  the  extract  from  the  patent  literature,  the  salt 
obtained  was  easily  oxidizable.  The  content  of  water  was  not 
investigated.  Also  the  reference  as  given  in  Dammer,1  is  that 
the  salt  changes  slightly  in  the  air  (as  the  salt  with  7H2O)  not 
that  it  is  unaltered. 

For  continuous  electrolysis  it  must  be  observed  that  from 
time  to  time  concentrated  sulphuric  acid  must  be  added  to  the 
cathode  fluid,  and  the  anode  fluid  moreover  diluted,  or  it 
may  be  partially  replaced  by  water,  or  the  conductivity  will 
reach  a  very  low  value. 

(2)  Chromic  Oxide  Compounds. 

O)    BY  ELECTROLYSIS  OF  AQUEOUS  SOLUTIONS. 

Bunsen  says  that  by  the  electrolysis  of  chromic  salt  solu- 
tions under  certain  conditions,  not  metallic  chromium  but  a 
chromous  oxide  compound  appears  at  the  cathode  (see  page  2). 

Lately,  however,  J.  Feree2  has  proven  that  there  must  be 
some  error  here.  The  important  results  of  his  investigation 
are  as  follows  : 

The  oxide  of  Bunsen  is  not  formed  when  a  mercury  cathode 
is  used  in  an  acid  solution  of  chromic  chloride,  no  matter  what 
current  density  is  used.  With  weak  current  densities  only 
hydrogen  is  evolved  at  the  cathode  ;  again  with  a  current 
density  of  0.025  ampere  per  square  centimetre  of  mercury  sur- 
face no  precipitate  appears. 

If  a  neutral  solution  of  chromic  chloride  is  electrolyzed,. 
even  at  high  current  densities,  there  appears  no  precipitate  of 
chromium,  so  that  the  earlier  published  investigations  on  the 
preparation  of  chromium  amalgam  electrolytically,  from  neu- 
tral solutions,  evidently  must  have  been  in  error.  On  the 
contrary  there  is  formed  in  the  electrolyte  a  black  powder 
with  the  qualities  which  Bunsen  ascribed  to  his  chromous- 
chromic  oxide.  It  can  be  easily  obtained  in  large  quantities 
if  a  platinum  cathode  is  used,  by  the  electrolysis  of  a  solution 
containing  160  grams  of  crystallized  chromic  chloride  per 
liter. 

1  Loc.  cit. 

2  Bulletin  Soc.  Chim.  de  Paris  [3],  25,  620  (1901). 


OXYGEN    COMPOUNDS.  77 

Returning  to  the  opinion  of  Bunsen,  it  has  been  shown 
qualitatively  that  the  material  was  pure  chromium  hydroxide ; 
a  certain  amount  which  had  lain  for  some  time  in  a  vacuum 
over  sulphuric  acid  was  put  in  a  tube,  which  was  exhausted 
and  sealed.  When  the  lower  part  of  the  tube  was  heated  in 
an  oil-bath,  it  was  observed  that  at  80°  water  vapor  was 
evolved  which  condensed  in  the  colder  part  of  the  tube  ;  at 
400°  the  black  contents  of  the  tube  glowed  strongly  and  be- 
came green.  The  vacuum  was  not  changed,  for  on  heating 
one  place  to  redness  it  flattened  out;  the  change  had  also 
taken  place  without  the  admission  of  oxygen. 

From  the  experiment  it  may  be  concluded  that  no  evolu- 
tion of  oxygen  had  taken  place  during  the  change,  yet  the 
latter  fact  was  proved  by  a  separate  investigation. 

The  analysis  of  the  material  gives  the  formula  Cr2O3.H2O, 
and  the  transformation  consisted  only  in  the  change  of  the 
black  modification  of  the  material  into  the  green  oxide. 

The  brownish  black  powder  is  formed  also  by  the  electrol- 
ysis of  a  neutral  chrome  alum  solution.  It  is  insoluble  in 
acids  but  is  easily  attacked  by  nitric  acid  and  potassium 
chlorate  (mixture  of  both  ?).  On  being  heated  in  the  air  it 
changes  to  the  green  modification. 

In  the  above-described  preparation  of  chromic  oxide  the 
current  exerts  neither  an  oxidizing  nor  a  reducing  influence ; 
it  acts  by  forming  on  the  cathode  an  excess  of  OH  ions,  that 
is  to  say,f produced  alkali,  which  in  turn  reacts  on  the  dis- 
solved chromium  salt  and  forms  the  insoluble  oxide.  It  is 
therefore  clear  that  the  electrolysis  of  an  acid  solution  would 
be  without  result,  and  also  that  the  material  of  the  cathode 
was  without  influence  at  least  as  far  as  the  description,  accord- 
ing to  which  mercury  or  platinum  cathode  may  be  used  in- 
differently^allows  us  to  infer. 

Chromic  oxide  can  also  be  prepared  by  using  the  reducing 
effect  of  the^current  on  an  alkaline  chromate  solution  ;  this  is 
the  reaction  which  occurs  in  the  spontaneous  working  of  the 
chromic  acid  element,  by  which  reaction  electrical  energy  is 


78  CHROMIUM  AND  ITS  COMPOUNDS 

obtained.  The  achievement  of  a  high  current  output  in  the 
technical  operation  of  this  process  lies  in  keeping  within  cer- 
tain working  conditions  which  G.  Street  has  made  the  object 
of  several  patents.1 

If  a  cold  alkali  chromate  solution  is  electrolyzed  between 
platinum  electrodes  only  a  very  moderate  amount  of  oxide  is 
obtained,  the  amount  being.only  slightly  increased  on  heating 
the  electrolyte  up  to  75°. 

If  a  mercury  cathode  is  substituted  for  the  platinum  cathode^ 
and  the  temperature  of  the  electrolyte  is  kept  between  70° 
and  80°,  chromic  oxide  is  formed  at  once  which  remains  sus- 
pended in  the  electrolyte.  The  process  is  carried  out  as  fol- 
lows :  An  aqueous  10  per  cent,  (weight)  solution  of  chromate 
is  electrolyzed  between  a  temperature  of  70°  and  80°,  pref- 
erably without  the  use  of  a  diaphragm.  An  electromotive 
force  of  4  volts  and  a  current  density  of  0.05  ampere  per  square 
centimetre  of  cathode  surface  and  4  amperes  per  square  centi- 
metre of  anode  surface  should  be  used. 

It  is  known  that  the  sodium  amalgam  formed  effects  the  re- 
duction of  the  chromic  acid  to  chromic  oxide,  though  doubt- 
less some  part  of  the  chromic  acid  is  transformed  primarily  into 
chromic  oxide  ;  the  advantage  which  the  mercury  shows  over 
the  platinum  lies  in  the  large  overvoltage  which  is  required 
to  set  free  hydrogen  from  mercury  cathodes.  The  chromic 
oxide  separated  out  no  longer  dissolves  in  the  soda  solution  at 
the  increased  temperature.  A  circulation  of  the  electrolyte 
increases  the  efficiency  of  the  reaction  ;  this  circulation  may 
be  accomplished  by  heating  as  well  as  by  the  rising  column  of 
gas  on  the  electrodes. 

The  chromium  content  can  be  quantitatively  separated  out 
as  chromic  oxide,  at  the  same  time  the  whole  of  the  sodium 
being  obtained  in  the  form  of  caustic  soda  solution.  Bichrom- 
ates can  be  used  in  the  place  of  chromates.  If  one  starts 
with  chromate,  then  bichromate  can  be  added  to  the  bath  in 
such  measure  as  the  oxide  is  separated  out ;  by  combination 

1  German  Patent  109,824,  June  n,  1899. 


OXYGEN    COMPOUNDS.  79 

with  a  corresponding  amount  of  alkali  the  bichromate  is 
changed  to  chromate.  These  additions  of  bichromate  are 
limited  only  by  the  concentration  of  soda  which  is  to  be  at- 
tained in  the  valuable  soda  solution  by-product.  Instead  of 
using  only  one  cell  the  electrolyte  can  be  circulated  through 
a  battery  of  cells. 

The  chromic  oxide  can  be  separated  from  the  solution  by 
simple  decantation. 

The  remark  that  the  platinum  anode  could  be  replaced  by 
mercury  ought  not  to  be  taken  in  earnest.  Since  in  this  case, 
as  was  remarked,  there  is  formed  an  insoluble  mercury  chrom- 
ate, which  would  entail  a  high  electromotive  force  were  it 
also,  as  remarked,  possible  to  decompose  it  into  mercury  and 
chromic  oxide  by  a  mere  reversal  of  current,  but  which  as  we 
will  soon  see  is  not  at  all  the  case. 

Patent  Claim. 

Process  for  the  electrolytic  preparation  of  chromic  oxide 
from  alkali  chromates,  characterized  by  the  application  of 
mercury  as  cathode  material. 

In  a  note  Strameo1  mentions  that  he  has  tested  and  con- 
firmed Street's  remarks  relative  to  the  better  working  of  mer- 
cury electrodes  ;  on  the  contrary  he  found  that  by  the  use  of 
two  mercury  electrodes  the  change  of  mercury  chromate  to 
mercury  and  chromic  oxide  did  not  take  place  ;  there  ap- 
peared only  mercury,  and  the  simultaneous  formation  of 
chromic  oxide  first  began  after  the  complete  disappearance  of 
the  mercury  chromate. 

It  is  also  to  be  noticed  further  on  in  the  remarks,  that 
along  with  the  usual  product,  the  hexahydrate,  also  the  tetra- 
hydrate  Cr2O(OH)4,  the  so-called  Guignet's  green  is  formed, 
which  is  insoluble  in  acids  and  extraordinarily  valuable  as 
pigment,  but  the  amount  of  it  if  the  directions  of  Street  are 
followed  is  only  i  to  2  per  cent.  It  is  formed  more  abun- 
dantly if  the  solution  is  kept  rich  in  alkali  and  poor  in 
chromate. 

1  L'Electricita  2O,  627  (1901). 


80  CHROMIUM  AND  ITS  COMPOUNDS. 

Finally  the  possibility  is  referred  to  of  preparing  all  chrom- 
ium salts  by  adding  the  desired  acid  in  the  manner  of  the 
above  method.  For  instance  if  a  nitric  acid  solution  of  so- 
dium chromate  is  electrolyzed,  the  chromium  will  be  com- 
pletely changed  to  chromium  nitrate,  along  with  which  there 
is  present  in  the  solution  only  sodium  nitrate.  But  it  should 
be  here  noted  that  this  "  possibility"  is  not  well  founded,  be- 
cause the  greater  part  of  the  oxide  will  be  again  oxidized  to 
chromic  acid  at  the  anode.  Only  so  long  as  one,  like  Street, 
works  with  an  alkaline  solution  in  which  the  chromic  oxide 
is  insoluble,  can  the  regeneration  to  chromate  practically  be 
neglected,  in  case  the  aid  of  a  diaphragm  is  not  employed. 
Regarding  the  many  theoretical  phantasies  to  be  found  in 
this  article  we  need  not  pay  them  further  attention. 

On  the  above  subject  there  are  still  several  interesting  ob- 
servations made  by  Reese1  on  the  reducing  action  of  electro- 
lytically  generated  hydrogen  on  chromic  acid.  He  arranged 
the  two  platinum  electrodes  one  above  the  other,  the  cathode 
on  the  bottom  of  a  burette,  and  the  anode  at  the  point,  so  that 
the  hydrogen  had  to  pass  through  the  whole  length  of  the  solu- 
tion, while  the  oxygen  could  escape  directly.  Using  perfectly 
pure  chromic  acid  as  electrolyte,  and  electrolyzing  for  twenty- 
four  hours,  with  a  strong  evolution  of  hydrogen,  no  trace  of 
reduction  was  noticeable,  but  on  the  addition  of  a  small 
amount  of  a  sulphate  or  sulphuric  acid,  reduction  began  in  a 
short  time,  but  only  up  to  a  certain  amount,  which  was  in  one 
case  2.85  per  cent,  (reckoned  on  the  whole  solution).  A  like 
behavior  was  noticed  on  the  addition  of  sulphuric  acid,  potas- 
sium sulphate  and  chromium  sulphate. 

A  solution  of  pure  potassium  bichromate  acted  exactly  like 
the  solution  of  chromic  acid  ;  reduction  first  began  on  the 
addition  of  sulphuric  acid  or  sulphates. 

The  author  thinks  the  fact  that  chromic  acid  may  be 
reduced  to  a  varying  degree  according  to  its  content  of  sul- 
phuric acid  or  sulphates,  may  perhaps  serve  to  determine  the 
1  Amer.  Chetn.  Journal,  22,  162  (1899). 


OXYGEN   COMPOUNDS.  8 1 

amounts  of  those  substances  present  or  the  relative  strength 
of  the  acids  (?). 

It  has  almost  the  appearance  as  if  there  is  here  a  catalytic 
acceleration,  and  it  may  be  of  interest  to  know  that  work  will 
begin  in  my  laboratory  on  a  closer  study  of  these  facts.  (See 
also  the  remarks  of  Buff  further  on.) 

(£)    BY  THE  USE  OF  HIGH  TEMPERATURES. 

In  order  to  investigate  the  behavior  of  chromic  oxide  at 
high  temperatures,  Moissan1  put  ordinary,  pure,  anhydrous, 
pulverized  chromic  oxide  under  the  electrodes  of  an  electric 
furnace  and  sprung  an  arc  over  it.  The  carbon  electrodes 
were  previously  heated  to  a  high  temperature  in  a  current  of 
nitrogen. 

By  the  use  of  30  amperes  at  55  volts  he  obtained  a  black, 
shiny  wart-shaped  mass,  studded  with  groups  of  small  dark 
crystals,  which  when  treated  with  potassium  nitrate  and  pre- 
cipitated with  mercuric  nitrate  showed  an  average  content 
of  51.9  per  cent,  of  chromium,  corresponding  closely  to  the 
formula  CraO  .  These  crystals  were  very  hard  and  left  a  green 
streak  on  porcelain. 

Molten  chromic  oxide  combines  very  easily  with  calcium 
oxide,  and  Moissan  has  obtained  many  of  these  double  oxides 
by  heating  a  mixture  of  quicklime  and  chromic  oxide  in  vari- 
ous proportions  in  a  limestone  furnace,  using  the  purest  pos- 
sible carbon  electrodes  and  a  current  of  1000  amperes  at  50 
volts.  Along  with  dark  green,  needle-like  crystals,  often  sev- 
eral millimeters  long,  and  which  were  not  investigated  fur- 
ther, were  found  towards  the  termination  of  the  experiment,  in 
hollows  in  the  molten  cake,  small,  yellow,  lamellar,  trans- 
parent crystals,  which  were  slowly  decomposed  by  water. 
The  result  of  an  analysis  corresponded  very  nearly  to  the 
formula  Cr2O3.4CaO.  (See  also  page  3$) 

An  experiment  of  Moissan  is  also  worth  mentioning,  in 
which  he  added  a  little  chromium  oxide  to  aluminium  oxide, 
and  melted  the  mixture  in  a  carbon  crucible  with  25  to  30 

1  Ann.  de  Chimie  et  de  Physique  [7],  4,  136  (1895). 


82  CHROMIUM    AND   ITS    COMPOUNDS. 

amperes  at  50  volts.  By  this  treatment  small  red  crystals  of 
ruby  separated  from  the  mass,  which,  however,  were  very 
much  less  beautiful  than  those  of  Fremy  and  Verneuil.  The 
operation  lasted  only  ten  to  fifteen  minutes,  and  furthermore, 
since  at  this  temperature  the  aluminium  is  easily  volatilized, 
so  it  appears  quite  possible  to  obtain  beautiful  ruby  crystals 
in  this  way  without  much  trouble.  In  connection  with  this 
work,  Dufau1  has  later  made  a  thorough  investigation  on  the 
formation  of  double  oxides  of  chromium. 

Moissan,  in  his  work,  made  use  of  a  "  furnace  of  calcium 
carbonate  for  crucibles,"  in  the  interior  of  which  he  put  the 
mixture  of  pure  anhydrous  oxide,  which  had  just  before  been 
calcined  in  a  Pernot  furnace.  In  order  to  avoid  the  influence 
of  the  furnace  material,  the  lime,  the  bottom  of  the  cavity 
was  covered  with  a  layer  of  the  oxide,  mixed  with  chromic 
oxide,  on  which  the  mixture  was  poured,  and  which  was  then 
surrounded  with  a  wall  of  those  oxides. 

According  to  the  investigations  of  Le  Chatelier2,  it  was 
noticed  that  at  about  900°  chromic  oxide  changed  into  another 
form  with  a  noticeable  evolution  of  heat,  this  new  form  being 
insoluble  in  acids  and  at  440°  was  attacked  by  neither  sul- 
phur, hydrogen  sulphide,  chlorine,  or  oxygen.  This  change 
in  the  ordinary  chromium  oxide  took  place  in  the  whole  of 
subsequent  investigations. 

For  the  preparation  of  a  double  oxide  of  chromium-magne- 
sium a  mixture  of  150  grams  of  CraO3  and  40  grains  of  MgO 
was  put  in  the  furnace  and  heated  for  ten  minutes  with  a  cur- 
rent of  30x3  amperes  at  45  volts.  After  cooling  there  was 
found  a  greenish  brown,  crystalline,  partly  melted  mass, 
which  was  attacked  slowly  by  warm,  concentrated  hydro- 
chloric acid  with  an  evolution  of  chlorine,  which  denoted  the 
presence  of  chromate,  which  fact  was  also  easily  established 
by  treating  the  broken-up  mass  with  boiling  water.  If  this 
mass  is  treated  with  nitric  acid  until  no  more  dissolves,  then 

1  Ann.  de  Chimie  et  de  Physique,  [7],  12,  257  (1897). 

2  Bulletin  Soc.  Chim.  [2],  47,  303. 


OXYGEN   COMPOUNDS.  83 

the  crystallized  residue  forms  a  double  oxide,  contaminated 
by  lamellar  chromic  oxide,  the  whole  remaining  stable  at 
the  highest  temperatures  used.  By  repeated  trituration  (levi- 
gation)  separation  can  be  obtained  with  a  fair  degree  of  ease. 
There  remains  a  dark  green,  nearly  black,  crystalline  powder, 
which  under  the  microscope  appears  to  consist  of  small  octa- 
hedral crystals,  the  thinnest  being  of  a  beautiful  green  color 
by  transmitted  light  and  without  action  on  polarized  light. 
Their  density  was  4.6  at  20°,  their  hardness  higher  than  that 
of  quartz,  streak  bright  green ;  their  analysis  agreed  closely 
to  the  formula  Cr2O3.MgO. 

A  second  experiment,  using  50  volts  and  1000  amperes,  fur- 
nished a  brown,  well-fused,  very  hard  mass,  which  was  only 
attacked  by  acids  with  difficulty ;  the  carefully  separated 
crystals  were  also  octahedral,  and  showed  the  above-described 
characteristics.  Before  analysis  the  finely  ground  powder  was 
dried  in  a  vacuum  over  sulphuric  acid  ;  then  200  to  400  mm. 
of  the  material  were  placed  in  a  platinum  crucible  with  ten 
times  the  amount  of  a  mixture  consisting  of  4  parts  of  potas- 
sium nitrate  and  i  part  of  potassium  carbonate,  and  fused. 
The  decomposition  took  place  very  regularly  in  more  or  less 
time,  according  to  the  nature  of  the  oxides.  When  the  de- 
composition was  thought  complete  the  crucible  was  heated  to 
redness  and  allowed  to  cool.  By  treating  the  contents  with 
water  the  chromate  went  into  solution,  while  the  other  oxide 
remained  behind  as  a  carbonate. 

With  magnesium  chromite  especially,  the  decomposition 
was  somewhat  long,  over  half  an  hour.  The  estimation  of 
the  dissolved  chromate  and  the  precipitated  magnesium  oxide 
was  performed  in  the  usual  manner.  The  magnesium  chrom- 
ite showed  characteristic  reactions.  Boiling  sulphuric  acid 
dissolved  simultaneously  both  the  chromium  and  the  magne- 
sium ;  likewise  hydrofluoric  and  hydrochloric  acids  acted  in 
the  same  way,  but  more  slowly;  on  the  contrary  boiling  nitric 
acid  was  without  action,  as  also  chlorine,  bromine,  and  iodine. 
As  already  seen  in  the  analysis,  oxidizing  agents  acted  only 


84  CHROMIUM    AND    ITS    COMPOUNDS. 

slowly  ;  even  oxygen  at  redness  ;  on  the  contrary,  there  is 
always  formed  in  the  preparation  of  these  double  oxides  in 
the  electric  furnace  a  considerable  amount  of  magnesium 
chrornate.  Other  like  combinations  could  not  be  obtained  in 
the  electric  furnace  in  spite  of  variation  of  the  current 
strength. 

For  the  preparation  of  a  double  oxide  of  chromium  and 
calcium,  a  mixture  of  115  grams  of  calcined  chromic  oxide 
and  45  grams  of  unslaked  lime  was  heated  in  an  electric  fur- 
nace by  700  amperes  at  50  volts.  The  crystalline  product 
showed,  besides  yellow  laminae,  resembling  those  described 
by  Moissan  (see  preceding),  needles  several  millimeters  long, 
of  a  dark  color,  and  occurring  in  radiating  groups.  With  300 
amperes  at  45  voks  only  the  needles  and  not  the  yellow 
laminae  were  obtained. 

In  order  to  isolate  the  needles,  the  crystallized  parts  lying 
loose  in  the  furnace  were  treated  with  concentrated  hydro- 
chloric acid.  A  strong  reaction  took  place  with  a  simultaneous 
brown  then  green  coloration  of  the  solution  and  an  evolution 
of  chlorine.  After  this  had  stopped  the  treatment  was  con- 
tinued with  boiling  hydrochloric  acid  until  no  more  would 
dissolve.  Finally  the  adhering  crystallized  chromium  oxide 
was  separated  by  repeated  trituration  (levigation).  The  resi- 
due consisted  of  dark  green,  prismatic  needles,  with  metallic 
luster,  transparent  thin  sections  appearing  under  the  micro- 
scope a  beautiful  green.  Their  density  was  4.8  at  18°,  their 
hardness  close  to  6,  their  powder  bright  green.  The  analysis 
gave  results  corresponding  closely  to  the  formula  CrzO  .CaO. 
This  double  oxide  is  somewhat  resistant  to  chemical  reagents; 
fluorine  will  not  attack  it  when  cold  ;  however  it  will  with  a 
slight  rise  of  temperature  with  a  strong  glowing  and  the  evo- 
lution of  a  thick  yellow  smoke.  The  action  of  chlorine  at  a 
bright  red  heat  slowly  forms  calcium  chloride,  while  the 
chromium  oxide  does  not  appear  to  be  affected.  Bromine  and 
iodine  do  not  react.  The  calcium  chromite  is  easily  suscepti- 
ble to  oxidation  ;  a  part  is  changed  to  chrornate  when  it  is 


OXYGEN    COMPOUNDS.  85 

powdered  and  heated  to  100°  in  air.  In  oxygen  it  burns 
quickly  at  the  temperature  at  which  glass  softens.  It  is  unaf- 
fected by  solutions  of  hydrofluoric  and  hydrochloric  acids  and 
by  concentrated  nitric  and  sulphuric  acids.  Anhydrous  hy- 
drofluoric acid  forms  calcium  fluoride  and  amorphous  chromic 
oxide  at  a  red  heat,  hydrochloric  acid  gas  performing  a  simi- 
lar reaction  with  glowing.  Of  oxidizing  agents  potassium 
chlorate  is  the  most  effective. 

Collectively,  the  earlier  investigations  of  Moissan  can  be 
stated  thus  :  With  the  application  of  300  amperes  at  45  volts 
the  chromite,  CraO3.CaO,  is  formed;  with  700  amperes  at  50 
volts,  and  so  at  a  higher  temperature  a  second  compound  is 
also  formed,  CraO  .zj-CaO,  which  predominates  when  1000  am- 
peres at  50  volts  is  used. 

Strontium  chromite  is  not  stable  at  high  temperatures  ;  it 
appears  to  be  more  easily  oxidized  than  calcium  chromite. 
If  an  intimate  mixture  of  strontium  oxide  and  chromic  oxide 
is  subjected  to  the  heating  action  of  an  arc  of  50  amperes  at  50 
volts  or  one  of  300  amperes  at  55  volts,  a  green  crystalline  mass  is 
obtained,  which  appears  to  consist  of  only  chromate  and  crys- 
tallized chromium  oxide.  Stronger  electric  currents  have 
the  same  effect. 

The  following,  on  the  contrary,  were  the  results  with 
barium  oxide,  in  which  a  very  high  chromium-content 
double  compound  was  formed.  On  a  ten-minute  treatment  of 
a  mixture  consisting  of  equal  parts  of  both  oxides,  with  a  cur- 
rent of  300  amperes  at  50  volts,  there  was  found  in  the  fur- 
nace a  fused  green  mass  with  a  crystalline  fracture,  and  which 
was,  as  before,  treated  with  hydrochloric  acid;  a  lively  reaction 
also  took  place  here,  coloring  the  solution  brown  and  then 
green,  with  an  evolution  of  chlorine.  After  treating  until  no 
more  would  dissolve,  there  remained  a  mass  of  crystals.  If 
the  solution  is  shaken  up,  dark  shining  crystals  of  the  double 
oxide  first  settled  down  and  on  them  the  green  laminae  of 
crystallized  chromic  oxide;  by  repeated  trituration  they  could 
be  separated.  This  double  oxide  formed  small,  black,  shining 


86  CHROMIUM    AND    ITS    COMPOUNDS. 

crystals,  which  made  a  brown  powder  of  a  slightly  greenish 
shade  ;  under  the  microscope  they  appeared  transparent  and 
hexagonal.  They  were  somewhat  harder  than  quartz;  at  15° 
their  density  was  5.4.  They  were  unattacked  by  hydrofluoric 
hydrochloric,  nitric,  or  sulphuric  acids. 

Chlorine  and  bromine  acted  slowly  at  red  heat  with  the 
formation  of  the  corresponding  barium  haloid,  while  the 
chromium  oxide  did  not  appear  to  have  been  affected  ;  iodine 
had  no  effect.  In  oxygen  barium  chromate  was  formed  below 
a  fed  heat  with  a  bright  incandescence;  it  was  on  the  whole 
easily  oxidizable  like  calcium  chromite.  Water  and  sulphur 
vapors  were  without  effect  even  at  a  bright  red  heat ;  anhy- 
drous, gaseous  hydrofluoric  and  hydrochloric  acids  reacted  very 
slowly  at  redness  with  the  formation  of  the  respective  barium 
compounds. 

The  results  of  an  analysis  showed  the  compound  to  agree 
very  closely  with  the  formula  4Cr2O3.BaO. 

(3).    Chromic  Acid   Compounds. 

O)  CHROMATES  OF  THE  HEAVY  METALS. 

An  American  patent1  has  been  granted  to  Arthur  B.  Browne, 
in  which  the  electric  current  is  used  in  so  far  as  concerns  the 
preparation  of  the  necessary  alkaline  chromate.  The  patent 
itself  was  not  accessible  to  me,  so  a  reproduction  of  the  patent 
claims  must  suffice.2 

Patent  Claim. 

(i)  The  process  of  manufacturing  chromate  of  lead  which 
consists  in  first  producing  a  solution  of  a  soluble  salt  of  lead, 
as  the  nitrate,  acetate,  or  chloride,  simultaneously  preparing 
a  solution  of  chrome  alum,  precipitating  chrome  hydrate 
therefrom,  mixing  said  chrome  hydrate  with  an  excess  of 
caustic  alkali  to  redissolve  it,  mixing  the  resulting  strongly 
alkaline  solution  with  a  solution  of  common  salt,  passing  an 
electric  current  through  combined  solutions  to  produce  a  mix- 
ture of  bichromate  and  chromate  of  potash,  mixing  said  com- 

1  U.  S.  Patent  538,998,  April  18,  1894. 

*  Official  Gazette  of  the  U.  S.  Patent  Office,  71,  871  (1895). 


OF  THE 

UNIVERSITY 

^k  OF 

OXYGEN   COMPOUNDS.       *£|  87 

bined  bichromate  and  chromate  of  potash  with  said  solution 
of  a  soluble  salt  of  lead  to  precipitate  lead  chromate  and  wash- 
ing it  with  water,  refiltering  it  to  remove  the  water,  and 
finally  drying  the  resulting  product. 

(2)  The  process  of  manufacturing  chromate  of  lead  which 
consists  in  first  producing  a  solution  of  a  soluble  salt  of  lead,  as 
the  nitrate,  acetate  or  chloride,  simultaneously  preparing  a  solu- 
tion of  chrome  alum,  precipitating  chrome  hydrate  therefrom, 
filtering  said  chrome  hydrate  and  washing  it,  then  mixing  said 
filtered  chrome  hydrate  with  an  excess  of  caustic  alkali  to  re- 
dissolve  it,   mixing  the  resulting  strongly  alkaline  solution 
with  a  solution  of  common  salt,  passing  an   electric  current 
through   said   combined  solutions   to   produce   a   mixture  of 
bichromate  and  chromate  of  potash,  mixing  said   combined 
bichromate  and  chromate  of  potash  with   said   solution  of  a 
soluble  salt  of  lead  to  precipitate  lead  chromate,  filtering  said 
lead  chromate  and  washing  it  with  water,  refiltering  it  to  re- 
move the  water  and  finally  drying  the  resulting  product. 

(3)  The  process  of  manufacturing  chromate  of  lead,   which 
consists  in  first  producing  a  solution  of  a  soluble  salt  of  lead, 
as  the  nitrate,  acetate  or  chloride ;  simultaneously  producing 
a   solution    of    a    mixture   of   bichromate   and   chromate    of 
potash,  by  passing  an   electric  current  through   an  alkaline 
solution  of  chrome  hydrate ;  mixing  said  solution  of  a  mix- 
ture of  bichromate  and  chromate  of  potash  with  said  solution 
of  a.  soluble  salt  of  lead,  to  precipitate  lead  chromate ;  filter- 
ing said  lead  chromate  and  washing  it  in  water,  refiltering  it 
to  remove  the  water,  and  finally  drying  the  resulting  product. 

In  the  patent  specifications  of  one  English  and  two  German 
patents  of  C.  Luckow,  which  are  concerned  with  the  electro- 
lytical  production  of  difficultly  soluble  salts  and  oxides,  we 
find  special  data  upon  the  manufacture  of  neutral  and  basic 
lead  chromates.  We  will  examine  the  patents  chronologically, 
and  take  out  of  them  what  would  interest  the  electrochemist. 

In  the  first  patent1  Luckow  will  practically  utilize  u  the 
theory  of  electrolytic  and  hydrolytic  dissociation "  in  the 
1  German  Patent  91,707,  Dec.  4,  1894. 


88  CHROMIUM    AND   ITS    COMPOUNDS. 

manufacture  of  difficultly  soluble  salts  or  oxides,  from  solu- 
ble metallic  anodes ;  he  employs  for  this  purpose  only  electro- 
lytes, which,  as  he  says,  may  be  considered  as  dissociated 
either  electrolytically  or  hydrolytically  or  electrolytically  and 
hydrolytically.  The  maximum  of  dissociation  appears  to  be 
different  for  different  salts,  fluctuating,  however,  for  the  in- 
vention concerned  somewhere  between  0.3  and  3  per  cent,  of 
dissolved  salt  (calculated  on  anhydrous  salt);  the  use  of  1.5 
per  cent,  of  dissolved  salt  usually  suffices.  Better  results 
were  obtained  in  this  way  with  the  use  of  considerably  less 
current  consumption  than  was  possible  with  the  electrolytic 
processes  hitherto  proposed  for  the  same  or  similar  purposes. 
Luckow  apparently  only  slightly  understood  this  new  theory 
at  that  time ;  the  maximum  of  dissociation  of  the  salts  in 
question  (sodium  chlorate,  sodium  carbonate,  etc.),  is  at  in- 
finite dilution,  while  the  maximum  of  conductivity  in  the 
same  case,  if  one  chooses  them  for  the  maximum  economy  of 
energy,  lies  with  the  much  higher  concentration. 

Further  Luckow  says  that  the  desired  reactions  take  place 
much  better  if  a  mixture  of  salts  is  used,  and  mixtures  of 
about  80  to  99.5  of  the  one  to  20  to  0.5  of  the  other  by 
weight  are  the  most  suitable.  For  the  preparation  of  salts  in 
general,  a  salt  which  forms  an  easily  soluble  compound  with 
the  anode,  composes  80  per  cent,  of  the  mixture,  and  the  re- 
maining 20  per  cent,  of  such  acids  which  will  form  a  diffi- 
cultly soluble  combination  with  the  anode  material. 

In  most  cases  salts  of  the  alkalies  (ammonia  included)  and 
the  alkaline  earths  are  suitable.  The  electrolyte  should  be 
"as  far  as  possible  neutral,  that  is,  slightly  acid,  slightly  alka- 
line, or  neutral,"  and  its  composition  should  be  kept  as  nearly 
constant  as  possible ;  also  the  dissolving  anode  should  be  re- 
newed when  the  consumption  has  reduced  it  to  1.5  milli- 
metres thickness. 

"  For  electrodes  there  are  used  for  each  square  metre  of 
anode  surface  eight  positive  and  nine  negative  electrodes, 
which  are  hung  15  mm.  apart  in  a  space  200  mm.  high  and 


OXYGEN    COMPOUNDS.  89 

300  mm.  wide,  and  whose  method  of  suspension  allows  a  sur- 
face contact  of  4  square  metres  with  the  electrolyte.  The 
material  of  the  anode  varies  according  to  the  desired  product; 
the  material  of  the  cathode  is  preferably  the  same  as  the 
anode,  but  it  can,  however,  be  different  from  it.  It  is  advis- 
able to  hang  the  cathode  in  a  bag  of  thin  woven  material. 

"  The  electromotive  force  required  depends  on  the  mix- 
ture of  salts ;  for  weak  acid  electrolytes  it  is  between  1.3  and 
1.5  volts,  for  neutral  about  1.8  volts,  and  for  feebly  alkaline 
about  2  volts." 

About  0.005  ampere  per  square  centimetre  is  recommended 
as  the  current  density.  The  temperature  should  not  rise 
above  50°.  To  avoid  interruptions  in  running,  the  purest 
possible  materials  should  be  used.  The  following  special 
directions  are  given  for  the  manufacture  of  lead  chromate  : 

Neutral  Lead  Chromate. 

For  electrolyte  use  a  i  y2  per  cent,  aqueous  solution  of  a 
mixture  of  80  parts  by  weight  of  sodium  chlorate  with  20 
parts  by  weight  of  sodium  chromate. 

The  anode  is  made  of  soft  lead,  the  cathode  of  hard  lead. 
The  electrolyte  is  neutral.  The  tension  is  1.8  volts.  The 
current  density  is  0.5  ampere  per  square  decimeter.  During 
electrolysis  the  electrolyte  is  kept  neutral,  and  water  and 
chromic  acid  must  be  carefully  introduced. 

Acid  Lead  Chromate. 

The  electrolyte  consists  of  a  i  y2  per  cent,  aqueous  solution 
consisting  of  a  mixture  of  80  parts  by  weight  of  sodium  chlo- 
rate and  20  parts  by  weight  of  sodium  bichromate. 

The  electrolyte  is  slightly  acid.  The  electromotive  force 
is  1.5  volts.  The  current  density  is  0.5  ampere  per  square 
decimeter.  During  electrolysis  the  electrolyte  is  kept  feebly 
acid  and  water  and  chromic  acid  must  be  carefully  added. 

The  patent  claims  in  question  read  : 

(i)  Process  for  the  production  of  salts  and  oxides,  which 
are  insoluble  or  soluble  with  difficulty  in  water  or  dilute, 


90  CHROMIUM    AND    ITS    COMPOUNDS. 

neutral  or  slightly  acid  or  slightly  alkaline  salt  solutions,  by 
means  of  electrolysis  from  a  suitable  metallic  anode,  charac- 
terized by  the  use  of  electrolytes,  which  have  been  brought 
into  the  condition  of  electrolytic  or  hydrolytic,  or  hydrolytic 
and  electrolytic  dissociation  near  the  neutralization  point,  and 
by  supplying  the  materials  separated  out  in  the  electrolysis  to 
keep  the  composition  of  the  bath  as  near  as  possible  constant, 
for  the  purpose  of  exerting  a  good  influence  on  the  consump- 
tion of  current  and  course  of  the  reactions. 

(4)  The  process    characterized   by  claim  i  applied  to  the 
production  of  neutral  lead  chromate  as  follows  :    A  neutral 
solution  of  a  mixture  of  sodium  chlorate  and  sodium  chromate 
is  subjected  to  electrolysis  between  lead  electrodes,  with  a  cur- 
rent density  of  0.5  ampere  per  square  decimeter,   with  addi- 
tions of  water  and  chromic  acid. 

(5)  The   process  characterized  by  claim   i  applied   to  the 
production  of  acid  lead  chromate  as  follows  :    A  slightly  acid 
solution  of  a  mixture  of  sodium  chlorate  and  sodium  bichrom- 
ate is   subjected   to  electrolysis  between  lead  electrodes,  with 
a  current  density  of  0.5  ampere   per  square  decimeter,  with 
additions  of  water  and  chromic  acid. 

In  the  second  patent1  the  process  in  question  is  elaborated. 
In  the  previously  patented  process,  the  electrodes,  particularly 
the  anode,  was  made  of  massive  material,  and  the  insoluble 
or  slightly  soluble  compounds  formed  did  not  stick  on  the 
anode  during  the  operation,  as  they  were  formed,  but  they 
rolled  off  the  surface  of  the  anode  in  dense  clouds  into  the 
depths  of  the  bath,  where  they  collected  together  on  the  bot- 
tom in  the  form  of  an  extremely  fine  powder  ;  concerning  the 
obtaining  of  chemical  compounds,  it  is  just  the  opposite  of 
that  which  is  desired  in  the  operation  of  the  manufacture  of 
the  electrodes  for  electrical  accumulators.  In  the  improved 
process  metallic  conducting  frames  were  prepared  in  such  a 
manner  as  to  hold  on  them  insoluble  or  slightly  soluble 
oxides,  salts,  metals  or  ores,  in  a  finely  divided  state  as  the 

1  German  Patent  105,143,    Sept.  4,  1895  (compare  also  the  supplemen- 
tary German  Patent  99,121,  May  13,  1897). 


OXYGEN   COMPOUNDS.  91 

soluble  material,  so  that  the  insoluble  or  slightly  soluble  end- 
products  would  remain  upon  or  in  these  electrode  frames  dur- 
ing the  operation.  The  preparation  of  the  electrodes  and  the 
operation  of  the  process  is  the  same  as  in  the  preparation  of 
electrodes  for  storage  cells  whose  ribs  and  grating  frames  are 
filled  with  metallic  dust,  or  coated  with  insoluble  or  difficultly 
soluble  oxides  or  salts  as  the  effective  (active)  material. 

For  electrodes  a  special  woven  wire  net  with  the  narrowest 
possible  meshes  was  employed ;  meanwhile  the  accumulator 
industry  has  invented  a  number  of  new  practicable  forms  of 
electrodes  which  can  be  used  for  this  purpose.  To  protect 
the  metallic  ribs  in  case  they  are  made  of  a  metal  easily 
alterable,  it  is  possible  to  polish  them  with  graphite  or  to 
platinize  them. 

After  the  pasty  mass  has  been  kneaded  or  pasted  into  the 
grooves,  it  is  surrounded  with  a  tightly  stretched  bag  of  filter 
cloth  or  like  material.  The  electrodes  should  be  spaced  20 
millimeters  apart. 

Concerning  the  electrolyte,  according  to  patent  No.  91,707, 
one  anion  causes  the  solution  of  the  massive  anode,  forming 
an  easily  soluble  salt  of  the  anode  metal,  the  other  transforms 
the  anode  metal  into  the  desired  insoluble  or  difficultly  solu- 
ble compound  ;  "  it  is  self-evident  that  the  first  anion  performs 
the  function  of  preventing  the  precipitated  insoluble  or 
slightly  soluble  compound  formed  on  the  anode  from  adher- 
ing to  it.  Which  constituent  must  have  predominating  in- 
fluence is  determined  by  the  nature  of  the  product  to  be  ob- 
tained." 

This  remarkable  fact  deserves  explanation.  How  is  it  for 
instance  that  by  the  electrolysis  of  a  mixture  of  sodium 
chromate  and  chlorate  between  lead  electrodes  a  beautiful 
precipitate  of  lead  chromate  is  formed  in  the  electrolyte,  and 
the  anode  dissolves  easily,  while  the  solubility  of  the  anode 
weakens  and  it  is  finally  covered  over  with  an  adhering  coat 
when  the  pure  sodium  chromate  solution  alone  is  used? 


92  CHROMIUM    AND   ITS   COMPOUNDS. 

Perhaps  this  action  depends  on  the  increase  of  solubility 
which  lead  chromate  would  certainly  show  in  a  solution  con- 
taining a  large  excess  of  sodium  chlorate.  It  is  accomplished 
by  the  formation  of  a  non-dissociated  lead  chlorate.  This  in- 
creased solubility  allows  a  somewhat  relatively  increased  super- 
saturation  of  chromate  of  lead,  and  so  prevents  the  formation 
of  a  dense  adhering  coat  of  lead  chromate  directly  on  the 
anode. 

With  these  explanations,  advanced  reservedly,  agrees  the 
fact  that  the  current  density  is  normally  low ;  the  formation 
of  an  adhering  coat  on  the  anode  is  to  be  feared  using  a  high 
density.  An  exhaustive  experiment  which  meanwhile  has 
been  worked  in  my  laboratory,  has  furnished  another  explana- 
tion for  the  above  phenomena.  The  results  may  be  found  in 
Zeitschr.  f.  Elektrochemie,  p.  255  (1902). 

In  the  more  generalized  process  the  salt  forming  the 
easily  soluble  compound  does  not  predominate  so  strongly, 
it  only  composes  one-half  to  two-thirds  of  the  mix- 
ture of  salts.  The  temperature  is  usually  kept  below  50°, 
without,  however,  excluding  higher  temperatures. 

The  current  density  is,  as  in  the  older  process,  preferably 
about  0.005  ampere  per  square  centimetre,  but  the  electro- 
motive force  is  higher,  lying  between  2  and  4  volts. 

Finally  there  remains  several  words  to  be  said  on  the  gen- 
eral method  of  operation,  etc.,  in  so  far  as  they  were  not 
stated  in  the  first  patent  specification. 

During  the  electrolysis  and  the  separation  of  the  ingre- 
dients out  of  the  solution  to  form  the  desired  product,  water, 
chromic  acid,  etc.,  must  be  added  in  such  a  manner  that  the 
concentration  and  the  neutrality  of  the  solution  is  not  ap- 
preciably changed.  On  the  other  hand,  the  accumulation  of 
impurities  and  deleterious  substances  is  to  be  avoided. 

The  introduction  of  a  current  of  air  or  steam  in  fine 
division  producing  a  good  stirring  without  bringing  the  elec- 
trolyte into  too  strong  agitation  has  a  good  effect. 

Basic  lead  chromate  (and  lead)  may  be  prepared  in  the  fol- 
lowing manner  : 


OXYGEN   COMPOUNDS.  93 

"  The  electrolyte  used  is  a  i  */£  to  2  per  cent,  aqueous 
solution  of  a  mixture,  consisting  of  two-thirds  sodium 
chlorate  and  one-third  sodium  chromate.  The  electrolyte 
is  made  slightly  alkaline  with  sodium  hydroxide.  The 
anode  frame  consists  of  platinized  hard  lead  and  the  cathode 
frame  of  either  hard  or  soft  lead.  The  filling  for  the  anode 
frame  is  composed  of  lead  dust  or  litharge,  that  of  the  cathode 
frame  of  red  lead  or  Phcenicochroite  (basic  lead  chromate). 
Should  the  cathode  charge  not  liberate  during  the  electrolysis 
a  sufficient  amount  of  chromic  acid  (which  may  be  expected) 
this  must  be  added  to  the  electrolyte." 

The  difficulty  with  this  process  plainly  lies  in  converting 
the  lead  powder  or  litharge  completely  to  chromate  ;  small 
pieces  are  completely  surrounded  by  chromate  and  insulated 
from  further  action.  At  least  to  convert  this  final  portion  a 
disproportionate  current  consumption  is  necessary,  if  a  pure 
material  is  desired.  Also  many  difficulties  are  introduced  in 
the  same  process  in  making  a  product  of  a  certain  sized  par- 
ticle, as  demanded  by  the  trade,  upon  which  depends  the 
shade  or  the  facility  of  reaction,  as  with  lead  peroxide  ;  this 
condition  is  considered  in  patent  No.  91,707. 

Patent  Claim. 

The  extension  of  the  process  protected  in  patent  No.  91,707 
to  the  manufacture  from  finely  divided  metals  and  ores  of  insol- 
uble or  slightly  soluble  oxides  or  salts  at  both  poles,  thereby 
characterized  by  the  filling  or  spreading  out  of  these  materials 
in  or  on  electrode  frames  of  metallic  conducting  material  and 
subjecting  them  to  the  action  of  the  electric  current  in  a 
highly  dilute  electrolyte  conformable  to  patent  No.  91,707. 

The  English  patent1  corresponds  to  the  two  German  patents 
in  contents.  Some  special  data  is  given  on  the  preparation 
of  lead  and  copper  chromates. 

The  color  of  the  lead  chromate  depends  on  the  bath  ;  a  neu- 
tral electrolyte,  consisting  of  a  solution  of  alkaline  nitrate, 
acetate,  or  chlorate  with  alkaline  chromate  or  chromic  acid 

1  English  Patent  14,801,  Aug.  6,  1895. 


94  CHROMIUM    AND    ITS    COMPOUNDS. 

yields  with  lead  anodes  a  beautiful  chrome  yellow,  which  be- 
comes brighter  if  the  solution  begins  to  become  acid,  and 
redder  if  it  becomes  alkaline.  Slightly  acid  solutions  yield, 
therefore,  a  fiery  citron  yellow,  and  slightly  alkaline  solutions, 
a  beautiful  chrome  orange,  which  changes  to  a  chrome  red 
with  increasing  alkalinity. 

For  the  production  of  the  bright  chrome  yellow,  care  must 
be  taken  that  the  solution  at  the  anode  does  not  become  too 
acid,  or  this  may  become  covered  with  an  insoluble  coat  of 
oxide  or  peroxide  ;  the  gradual  addition  of  the  necessary 
amount  of  chromic  acid  or  chromate  is  to  be  recommended. 

For  the  production  of  chrome  orange  a  mixture  of  potassium 
perchlorate  and  chromate  is  used.  Chrome  red  is  obtained 
by  the  addition  of  more  alkali. 

The  cost  of  manufacture  of  100  kilograms  of  pure  chrome 
yellow  is  $17.50  to  $20*00,  and  of  100  kilograms  of  pure 
chrome  orange  about  $12.50.  Copper  chromate  can  be  pro- 
duced in  the  same  manner  by  using  copper  anodes.  The 
electrolyte  consists  of  a  mixture  of  either  an  alkaline  nitrate^ 
sulphate,  chloride,  or  chlorate  with  chromic  acid  or  a  soluble 
chromate.  If  the  solution  is  neutral  or  slightly  acid  a  brownish 
red  chromate  is  precipitated,  if  feebly  alkaline,  a  green.  By 
increasing  the  acidity  of  the  solution,  the  brownish  red  will 
become  brighter,  until  finally  with  too  much  acid  the  copper 
no  longer  precipitates.  With  increasing  alkalinity  the  green 
color  becomes  deeper  but  much  duller. 

A  very  dilute  solution  of  a  mixture  of  six  parts  of  sodium 
chlorate  with  one  part  of  sodium  bichromate  is  suitable  for 
the  preparation  of  the  red  chromate,  while  for  the  preparation 
of  the  green  chromate  a  dilute  solution  of  a  mixture  of  4 
parts  of  sodium  or  potassium  chloride  with  i  part  of  sodium 
chromate,  to  which  before  the  beginning  of  the  electrolysis  a 
little  alkali  is  added,  can  be  recommended.  The  necessary 
chromic  acid  for  the  operation  of  the  process  must  be  con- 
tinually supplied. 


OXYGEN   COMPOUNDS.  95 

The  current  density  must  be  so  regulated  that  no  free  oxy- 
gen is  evolved  on  the  anode ;  with  too  high  current  densities 
the  desired  product  is  not  precipitated  fine  enough. 

The  amount  of  free  alkali  or  free  acid  should  not  be  above 
i  y?  per  cent,  by  volume  of  the  solution,  and  the  concentra- 
tion of  the  salt  should  remain  between  0.3  and  3  per  cent,  by 
weight.  Great  stress  is  laid  on  these  conditions. 

A  greater  dilution  is  not  advisable  because  of  the  smaller 
conductivity  of  the  solution  ;  a  lesser  is  likewise  not,  because 
in  those  kinds  of  solutions,  particularly  if  they  contain  too 
much  alkali  or  acid,  the  anodes  are  oxidized  "  with  quickly 
decreasing  rapidity  and  more  superficially  and  irregularly ;  " 
moreover,  the  product  suffers  and  tends  to  become  crystalline. 
The  product  is  obtained  as  a  pure,  amorphous  and  finely 
divided  powder  only  when  the  solution  is  made  up  within  the 
above  given  limits. 

Patent  Claim. 

(1)  The  herein-described  process  for  the  production  of  in- 
soluble or  practically  insoluble  oxides  and  salts  from  very 
dilute  neutral,  slightly  acid  or  alkaline  solutions  essentially  as 
described. 

(2)  In  the  electrolytic  production  of  insoluble  or  practically 
insoluble  salts  or  oxides,  the  simultaneous  use  of  an  anode  of 
the  desired  metal  or  containing  it,  and  very  dilute  neutral,  or 
slightly  acid  or  alkaline  electrolyte,  essentially  as  described. 

As  far  as  I  know,  in  the  attempts  to  manufacture  chrome 
colors  on  a  large  scale  by  these  methods,  serious  technical 
difficulties  have  arisen.  Whether  their  solution  has  been  un- 
successful or  if  finally  the  processes  have  proven  unprofitable, 
I  know  nothing  of  there  lately  having  appeared  on  the  market 
large  quantities  of  electrolytically  prepared  chromium  colors. 

(b)   CHROMATES  OF  THE  ALKALI  METALS  AND  CHROMIC  ACID. 

Already  in  the  year  1886,  F.  Fitzgerald  attempted  to  solve 
the  problem  of  transforming  chromic  oxide  compounds  into 
chromic  acid  compounds  by  the  aid  of  the  electric  current,  in 


96  CHROMIUM   AND    ITS    COMPOUNDS. 

a  cheaper  way  than  formerly.  Evidently  he  had  in  view  the 
treatment  of  the  chromic  oxide  solutions  found  in  chromic 
acid  cells  after  their  exhaustion,  in  that  he  wished  to  produce 
simultaneously  at  the  cathode  metallic  zinc  from  a  part  of  the 
zinc  sulphate  occurring  in  the  solutions.  In  the  patent  spec- 
ifications1 is  given  several  detailed  statements. 

A  solution  containing  zinc  and  chromic  sulphate  (or  chromic 
chloride)  is  electrolyzed  preferably  by  the  use  of  lead  anodes, 
although  all  other  less  attackable  conductors  as  platinum  and 
carbon  (? !)  are  not  excluded.  Lead,  zinc,  or  the  like  can  be 
used  as  cathodes,  and  are  usually  suspended  in  an  acid  zinc 
sulphate  solution  or  a  solution  of  ammonium  alum  in  which 
zinc  oxide  is  dissolved.  A  diaphragm  separates  the  anode  and 
cathode  solutions.  The  electrolysis  is  continued  until  the 
dark-colored  anode  solution  has  become  bright  red.  The 
metallic  zinc  precipitated  on  the  cathode  can  be  melted  and 
in  this  way  separated  from  the  chromic  oxide  precipitated 
there  at  the  same  time. 

The  proposed  separation  of  zinc  in  this  manner  must  have 
been  attended  with  considerable  difficulty  and  expense. 

In  order  to  avoid  the  inconvenient  transportation  of  large 
quantities  of  fluid,  the  solutions  were,  after  exhaustion,  run 
into  a  large  reservoir,  precipitating  therein  chromium  and 
zinc  oxides  by  lime,  magnesia,  or  the  like,  the  supernatant 
liquid  run  off,  and  the  solid  residue  taken  to  the  chromic  acid 
regeneration  plant.  There  the  oxides  were  mixed  together 
and  either  dissolved  together  by  a  dilute  mineral  acid,  or  first 
treated  with  ammonia  or  a  boiling  solution  of  fixed  alkali,  to 
bring  the  zinc  into  solution,  and  then  to  dissolve  the  chrom- 
ium, a  weak  acid  or  the  cold  solution  of  a  fixed  alkali  was 
poured  over.  The  solutions  were  then  respectively  oxidized 
and  reduced  in  the  following  manner. 

The  patent  claim  reads  : 

( i )  The  herein-described  process  for  the  electrolytic  regenera- 
tion or  production  of  dissolved  chromic  acid  from  chromic 

1  English  Patent  5, 542,  April  21,  1886. 


OXYGEN   COMPOUNDS.  97 

salts,  which  result  by  the  reduction  of  this  acid  when  it  has 
been  used  for  the  production  of  oxygen  for  galvanic  elements, 
or  chlorine  for  bleaching  or  other  purposes. 

(2).  The  herein  described  process  for  the  electrolytical  re- 
generation or  production  of  dissolved  chromic  acid  from  the 
exhausted  or  reduced  solutions  of  this  acid  produced  in  the 
manufacture  of  chlorine  or  oxygen,  consisting  in  treating  the 
solution  with  a  base  which  precipitates  the  chromic  oxide 
and  also  zinc  oxide,  redissolving  the  precipitated  oxide  and 
converting  it  into  chromic  acid  by  electrolysis. 

A  note  of  K.  F.  Smith1  shows  the  preparation  of  alkali 
chromates  directly  from  chromite,  in  which  the  chromite  is 
intimately  mixed  with  molten  potash  and  the  mixture  elec- 
trolyzed  (see  also  page  36).  Although  he  has  used  this 
method  only  for  the  analytical  determination  of  chromium  in 
chromite,  the  method  is  of  great  practical  interest  and  serves 
as  an  intimation  of  the  production  of  chromates  by  the  aid  of 
the  electric  current  on  a  large  scale. 

In  the  first  experiments  a  current  of  one  ampere  was  used. 
After  fifteen  minutes  the  oxidation  of  the  mineral  appeared 
complete.  A  stronger  current  worked  poorly:  "Among 
other  things,  a  stronger  current  acted  principally  on  the  iron 
oxide  in  the  ore  and  affected  the  potash,  so  that  a  larger  or 
smaller  amount  of  the  metal  concerned  was  precipitated. 
The  above-mentioned  phenomena  appeared  after  a  partial  de- 
composition of  the  mineral  so  that  some  chromite  always  re- 
mained undecomposed." 

Finally  good  results  were  obtained  with  the  following 
method  of  operation  :  30  to  40  grams  of  caustic  potash 
were  melted  in  a  nickel  crucible  i  T/Q  inches  high  and  2  inches 
in  diameter,  and  heated  until  the  excess  water  was  driven 
off.  The  crucible  was  then  placed  on  a  heavy  copper  ring, 
which  was  connected  to  the  anode  of  a  battery,  the  finely 
ground  mineral  (o.i  to  0.5  gram)  was  placed  upon  the 
fluid  potash  and  a  platinum  rod  was  put  in  for  cathode.  The 

1  Berlin,  Ber.,  24,  2182  (1891). 


9$  CHROMIUM    AND    ITS    COMPOUNDS. 

crucible  was  kept  covered  during  the  analysis,  and  warmed 
gently.  Before  stopping  the  determination  the  current  should 
be  reversed,  because  metallic  iron  is  precipitated  on  the 
•cathode  and  surrounds  small  particles  of  the  ore,  protecting 
them  from  being  attacked.  By  reversing  the  current  the  lat- 
ter were  set  free  and  exposed  to  oxidation. 

We  have  already  shown  that  it  is  not  possible  to  use  more 
than  one  ampere  for  the  above  quantity  of  ore ;  after  thirty 
to  forty  minutes  the  ore  is  decomposed,  even  when  it  is  very 
resistant.  When  decomposition  is  complete  hydrochloric  acid 
will  dissolve  the  contents  of  the  crucible  completely.  Other- 
wise the  decomposition  is  not  complete.  The  chromate  can 
be  determined  in  the  aqueous  alkaline  filtrate  by  the  usual 
methods. 

A  treatise  by  C.  Haussermann1  is  concerned  with  the 
electrolytic  oxidation  of  alkaline  chromic  oxide  solutions. 
Haussermann  puts  a  solution  of  chromic  oxide  in  an  excess  of 
concentrated  caustic  soda  solution,  in  a  porous  clay  vessel, 
forming  an  anode  compartment,  and  then  puts  the  latter  in  a 
glass  vessel  filled  with  water,  which  forms  the  cathode  space. 
The  anode  is  a  platinum  sheet,  the  cathode  an  iron  sheet 
each  7  X  12  square  centimeters  effective  surface.  With  a 
current  strength  of  2  amperes  the  electromotive  force  finally 
dropped  to  5  volts.  Sodium  chromate  and  some  oxygen  were 
formed  at  the  anode,  while  at  the  cathode  caustic  soda  and 
hydrogen.  The  investigation  was  performed  without  external 
heating  and  was  interrupted  before  the  complete  oxidation  of 
the  chromite  and  showed  a  yield  of  0.563  grams  of  the 
original  sodium  compound  transformed  into  the  higher  oxide 
form  per  ampere  hour,  corresponding  to  a  current  output  of 
42  per  cent. 

Further,  this  method  of  procedure  was  applied  to  the  pre- 
paration of  bichromates  from  neutral  chromates,  in  which 
the  anode  space  was  charged  with  a  solution  of  58  grams 
of  Na2CrO4  in  0.5  liter  of  water.  With  a  current  strength  of 
1  Dingler's  Polytechnisches  Journal,  288,  161  (1893). 


OXYGEN   COMPOUNDS.  99 

between  2  and  3.5  amperes  the  electromotive  force  dropped 
finally  to  6  volts  ;  after  eight  and  one-half  hours  the  experi- 
ment was  interrupted.  An  evolution  of  oxygen  and  an  odor 
of  ozone  was  noticed  at  the  anode,  and  at  the  cathode  a  strong 
evolution  of  hydrogen  ;  the  cell  was  not  warmed.  The  solu- 
tion in  the  anode  space  after  some  time  became  red,  that  in 
the  cathode  space  yellow ;  this  last  appearance  was  "ascribed 
to  a  wandering  or  diffusion  of  the  neutral  chromate."  To 
prevent  misunderstanding  it  was  remarked  that  the  chromate 
ion,  CrO4,  which  is  negatively  charged  travels  toward  the 
anode  under  the  influence  of  the  current.  Only  by  diffusion 
can  a  small  amount  of  chromate  get  into  the  cathode  space. 
An  analysis  showed  at  the  end  of  the  electrolysis  in  the  cathode 
solution  14  grams  of  caustic  soda  and  only  0.4  gram  of  neu- 
tral chromate  ;  the  anode  liquor  after  evaporation  left  40 
grams  of  crystallized  Na2Cr2O7.2H2O.  In  case  the  soda  liquor 
is  returned  to  the  circuit  of  manufacture — to  lixiviate  the 
roasted  material — the  chromate  admixture  does  no  injury. 
Excess  of  caustic  soda  which  was  formed  in  the  previously  used 
lixiviation  of  the  roasted  material  containing  calcium  chro- 
mate by  aqueous  soda  solution,  does  not  act  injuriously,  and 
therefore  the  solution  obtained  by  lixiviation  of  the  roasted 
mass  and  containing  sodium  chromate  along  with  caustic  soda, 
can  after  concentration  without  further  preparation  be  sub- 
jected to  electrolysis  and  worked  over  into  bichromate. 

To  be  quite  clear,  let  the  old  process  for  the  preparation  of 
bichromate  be  briefly  compared  with  the  electrolytic  process 
of  Haussermann.  It  should  be  first  noticed  that  Hausser- 
mann  left  undecided  the  practical  utilization  of  the  transfor- 
mation of  sodium  chromite  into  chromate  in  the  electrolytic 
manner,  and  was  concerned  only  with  the  conversion  of 
chromate  into  bichromate. 

According  to  the  old  methods  of  Haussermann  as  we  have 
recently  described,  the  roasted  material  containing  the  calcium 
chromate  is  treated  with  an  aqueous  solution  of  sodium  car- 
bonate.1 Often  sodium  sulphate  solution  is  used,  thus  pre- 

4  may  have  been  employed. 


100  CHROMIUM    AND    ITS    COMPOUNDS. 

cipitating  insoluble  calcium  carbonate  and  forming  soluble 
sodium  chromate,  along  with  some  free  caustic  soda.  The 
solution  is  concentrated  after  nitration,  and  just  enough  sul- 
phuric acid  is  added  to  neutralize  the  caustic  soda,  and  trans- 
form the  neutral  chromate  into  bichromate.  With  the  proper 
concentration  conditions  the  greater  part  of  the  sulphates  are 
precipitated  in  the  anhydrous  form  while  the  bichromate  re- 
mains in  solution. 

According  to  the  new  process  the  alkaline  chromate  liquor 
is  placed  in  the  anode  compartment  of  a  cell,  and  the  cathode 
space  is  filled  with  pure  water.1  By  electrolysis  bichromate 
is  formed,  and  on  the  cathode  side  caustic  soda  solution,  of 
which  not  an  inconsiderable  part  gets  over  to  the  anode  side 
on  account  of  the  large  velocity  of  migration  of  the  OH  ions. 
After  the  completion  of  the  electrolysis  the  cathode  solu- 
tion or  at  least  a  part  of  it  shall  find  application  in  the  leach- 
ing of  the  roasted  material  in  place  of  a  part  of  the  soda  so- 
lution, where  it  then  transforms  the  calcium  chromate  into 
calcium  hydrate  and  dissolved  sodium  chromate,  which  latter 
is  again  placed  in  the  anode  compartment  of  the  electrolytic 
cell  for  further  oxidation. 

The  bichromate  solution  in  the  anode  compartment,  com- 
pletely free  from  sulphates,  may  be  used  directly  for  oxidation 
or  worked  up  into  solid  bichromate. 

It  is  perhaps  advisable  to  explain  just  what  part  the  electric 
current  plays  in  the  transformation  of  chromates  into  bichro- 
mates in  the  anode  compartment.  Aside  from  some  acces- 
sory processes  we  do  not  find  an  oxidation  taking  place,  but 
oxygen  is  evolved  quantitatively.  Thereby  the  electrolyte 
would  become  acid,  and  we  know  that  acid  hinders  the  re- 
action. The  current  decomposes,  therefore,  in  this  view,  neu- 
tral salt  only  into  base  and  acid.  Incidentally  it  may  be  re- 
marked that  according  to  the  investigations  of  Ostwald2 
chromic  acid  has  the  formula  H2CraO7. 

1  Naturally  not  to  be  recommended  in  practice  ;  it  is  customary  to  use  a 
not  too  concentrated  solution  of  sodium  carbonate. 

2  Zeitschr.  f.  Physikalische  Chemie,  2,  78  (i! 


OXYGEN    COMPOUNDS.  IOI 

Haussermann  has  claimed  a  great  deal  when  he  said : 
41  After  the  preceding,  there  can  be  no  doubt  that  the  applica- 
tion of  electrolysis  to  the  manufacture  of  alkali  bichromates 
involves  an  important  step  forward,  and  that  the  process  de- 
scribed, which  is  protected  by  patents,  will  become  an  im- 
portant factor  in  the  commercial  world." 

Nothing  has  been  done  with  the  patent,  and  there  is  noth- 
ing known  of  a  practicable  application  of  the  process. 

The  electrolysis  of  the  alkali  chromates  and  the  like  is,  as 
mentioned  before,  not  new,  for  Buff J  decomposed  dissolved 
neutral  potassium  chromate  in  1856.  He  was  influenced  to 
take  up  these  experiments  because  of  a  statement  of  Geuther, 
who  claimed  to  have  found  that  by  the  electrolysis  of  aqueous 
solutions  of  pure  chromic  acid,  hydrogen  and  chromium  were 
precipitated  at  the  cathode,  and  oxygen  at  the  anode  to  the 
extent  of  a  third  or  more  greater  than  should  be  expected 
from  the  amount  of  electricity  passing.  Buff  could  not  sub- 
stantiate these  claims ;  the  oxygen  evolved  always  corre- 
sponded to  Faraday's  law  and  also  the  hydrogen  when  using 
a  ten  per  cent,  solution  of  chromic  acid.  By  the  electrolysis 
of  a  five  per  cent,  solution  of  pure  chromic  acid  reduction  in- 
versely proportional  to  the  current  density  was  observed.  The 
addition  of  sulphuric  acid  increased  the  reduction.  By  the 
electrolysis  of  acid  potassium  chromate,  the  same  phenomena 
was  observed  as  with  chromic  acid.  These  results  agreed  in 
part  with  the  much  later  ones  of  Reese  (see  page  80). 

The  formation  of  bichromate  at  the  anode  by  the  electroly- 
sis of  a  neutral  chromate  was  not  established ;  it  can  only  be 
supposed  to  have  taken  place  from  the  remark  :2  "  the  solution 
in  the  region  of  the  positive  pole  gradually  became  red  and 
gave  an  acid  reaction." 

1  Ann,  derChemie  und  Pharmacie,  1O1,-I  (1857). 

2  In  an  article  by  Merges  [Cotnpt.  rend.  87,   15  (1878)]  the  remark  is 
found  that  by  the  electrolysis  of  potassium  chromate,  bichromate  is  formed 
at  the  anode  ;  and  it  was  also  noticed  that  chromic  acid  in  a  dilute  solution 
was  partly  reduced  by  the  electric  current  to  chromic  chromate. 


102  CHROMIUM    AND    ITS   COMPOUNDS. 

Potassium  bichromate,  according  to  the  method  of  R. 
Lorenz,1  can  be  made  directly  from  ferrochrome,  by  the  help 
of  the  electric  current.  He  made  the  ferrochrome  the  anode 
in  a  caustic  potash  solution,  and  for  cathode  used  a  porous 
copper  oxide  plate.  On  the  application  of  two  volts  terminal 
tension,  dense  red  streams  ran  down  off  the  anode  and  oxygen 
was  not  evolved,  even  with  a  considerable  rise  of  tension. 

Since  the  ferrochrome  consisted  of  about  equal  parts  of 
iron  and  chromium,  it  might  be  expected  that  along  with  the 
red  chromate  potassium  ferrate  would  be  formed.  This  was 
not  the  case.  The  clear  red  color  proved  that ;  the  iron  col- 
lected as  hydroxide  on  the  bottom  of  the  vessel  and  was 
scarcely  "detectable  in  the  solution. 

Two  years  later,  Heibling  obtained  a  patent  in  England, 
for  in  the  main  the  same  idea  as  Lorenz  had.2  He  used  as 
anode  an  alloy  of  iron  and 'chromium  containing  at  least  55 
per  cent,  of  chromium,  and  a  carbon  or  iron  cathode  in  an 
electrolyte  consisting  of  alkali  salts,  preferably  an  alkaline 
chloride.  He  surrounded  the  electrodes  with  bells  for  the 
separate  collection  of  the  hydrogen  and  chlorine,  which  later 
formed  the  materials  for  the  manufacture  of  pure  hydrochloric 
acid.  The  amount  of  chlorine  set  free  at  the  anode  corre- 
sponded to  the  loss  of  current  occurring  in  the  manufacture  of 
chromate.  The  iron  of  the  anode  was  changed  to  oxide. 

The  electromotive  force  required  for  the  electrolysis  is  1.5 
volts,  and  to  produce  i  kilogram  of  crystallized  sodium  bi- 
chromate (Na2Cr2O7  -f  2H2O)  required  an  energy  expenditure 
of  two  kilowatt  hours.  For  the  preparation  of  i  kilogram  of 
crystallized  sodium  bichromate  there  was  consumed  about 
1 100  ampere  hours,  corresponding  to  a  current  output  of  80 
per  cent. 

It  is  also  worth  noticing  that  in  case  the  anode  contains 
less  than  55  per  cent,  chromium,  both  iron  and  chromium 
will  be  simultaneously  oxidized  without  the  formation  of 

1  Zeitschr.  f.  anorgan.  Chem.,  12,  396  (1896). 

2  English  Patent  4,624,  Feb.  24,  1898. 


OXYGEN    COMPOUNDS.  103 

chromate.  If  the  alloy  contains  crystals  (of  nearly  pure 
chromium  ?)  in  its  interior,  at  the  end  of  the  operation  these 
can  be  fused  together  with  the  use  of  graphite  into  a  valuable 
by-product ;  in  this  way  chromium  practically  free  from  iron 
can  be  obtained. 

The  patent  claim  following  will  furnish  the  remaining  in- 
formation. 

1.  Apparatus    for   the   electrolytic    production    of    alkali 
bichromates,  consisting  of  electrolytic  cells,   containing  the 
solution  of  an  alkaline  salt,  as  a  chloride,  nitrate  or  caustic 
alkali,  and  anodes  of  chromium  or  a  chromium-iron  alloy  with 
a  content  of  over  55  per  cent,  of  chromium  and  any  suitable 
cathodes.     The  cells  are  arranged  in  a  descending  series  so 
that  the  electrolyte  can  flow  from  one  cell  to  the  other,  be- 
cause of  this  difference  of  level,  essentially  as  described. 

2.  Apparatus  for  the   electrolytic  production  of   alkaline 
bichromates,    consisting  of   electrolytic   cells,    containing    a 
solution   of    an  alkali  salt  as  a  chloride,  nitrate  or  caustic 
alkali,  and  anodes  of  chromium  or  a  chromium-iron  alloy  con- 
taining  over   55   per   cent,    of  chromium  and  any  suitable 
cathodes.     The  individual  electrodes  are  surrounded  by  sepa 
rate  collecting  bells,  which  are  intended  for  the  collection  of 
the  gases  chlorine  and  hydrogen  at  the  two  poles  to  utilize 
them  for  the  production  of  pure  hydrochloric  acid,  essentially 
as  described. 

3.  In  the  apparatus  described  for  the  production  of  alkaline 
bichromates  electrolytically,  the  arranging  of  a  number  of 
carbon  anodes  either  in  each  cell  or  in  each  division  of  many 
cells  for  the  purpose  of  facilitating  the  separation  of  chlorine 
from  the  electrolytes. 

With  the  exception  of  Fitz-Gerald  (page  95)  all  inventors 
have  attempted  the  production  or  regeneration  of  chromates 
in  alkaline  solutions.  Since  at  the  present  time  large  amounts 
of  sodium  chromate  in  sulphuric  acid  solution  are  used  for 
oxidation,  the  preference  for  performing  the  regeneration  in 
alkaline  solution  would  add  the  loss  of  sulphuric  acid  to  that 
of  the  soda. 


104  CHROMIUM    AND    ITS    COMPOUNDS. 

These  and  other  disadvantages  (high  tension)  were  as  stated 
in  the  patent  claim1  of  the  Hochst  Color  Works  "  to  be  avoided 
by  a  rational  process  which  in  a  large  plant  has  already  been 
proved  to  be  of  high  commercial  importance.  Starting  with 
a  solution  of  the  chromium  salt  in  the  desired  acid,  as  chrom- 
ium sulphate  in  sulphuric  acid,  and  always  with  the  solu- 
tion of  the  highest  electrical  conductivity,  100  grams  of  CroO3 
and  350  grams  of  H2SO  can  be  diluted  to  a  liter.  Both  the 
anode  and  cathode  spaces  of  the  lead:lined  vessel,  provided 
with  a  diaphragm,  are  filled  with  the  solution  (lead  plates 
serve  for  electrodes).  By  the  action  of  the  current  chromic 
acid  is  formed  on  ?he  anode  side,  and  hydrogen  is  evolved  on 
the  cathode  side.  A  change  takes  place  in  the  concentration 
of  the  sulphuric  acid  on  both  sides,  decreasing  on  the  cath.or 
side  and  increasing  on  the  anode  side.  The  oxidized  so*  ,^10^ 
can  be  used  in  manufacturing  without  further  treatment, 
going  back  again  to  chromium  oxide,  when  it  comes  back  to 
the  cathode  side,  the  old  cathode  liquor  being  now  placed  in 
the  anode  compartment.  The  cathode  solution  has  by  this 
second  operation  become  richer  in  sulphuric  acid  than  the 
anode  solution,  but  on  the  passage  of  the  current  this  excess  is 
transferred  from  the  first  to  the  second.  NQ  f.  umulation  of 
sulphuric  acid,  etc.,  takes  place  in  this  cyeir  operation  in 
which  the  solutions  are  brought  alternately  jn  the  anode  and 
cathode  compartments,  and  these  solutions  can  be,  used  for  a 
long  time  as  an  excellent  carrier  of  r^vgen,  with  practically 
no  loss  or  change  in  composition.  The  electronic?  ve  force 
with  a  current  density  of  0.03  ampere  per  square  Centimeter 
is  not  quite  3^  volts  at  50°."  '--., 

The  patent  claim  reads  : 

Process  for  the  regenejff-e^i  of  chromic  acid  fro  pi  solutions 
of  oxidized  chromium  --jo  ccmy  an  elects1  y tic  methoc1  ")iar- 
acterized  by  the  use  of  I,  o  gra  on  of  a  c  2O3<iiic  c  :ide  sa  £ts 
corresponding  acid,  as  ci  ';ed.  ..ulplr  nnot*  sulphuric  aciu,  as 
1  German  Patent  103,860,  June  12,  1898;  identic?-1  With  the  American 
Patent  630,612,  which  bears  the  lames  of  Le  Blanc  a»  tfReisenegger. 


OXYGEN   COMPOUNDS.  IO5 

both  anode  and  cathode  solutions,  but  alternated  in  this  way, 
that  the  solution  containing  the  chromic  acid  after  passing 
through  its  stage  of  usefulness  and  having  been  converted  to 
chromic  oxide  again,  is  returned  to  the  cathode  side,  the 
previous  cathode  solution  being  placed  in  the  anode  compart- 
ment. 

An  interesting  article  by  Regelsberger,  on  the  regeneration 
of  chromic  acid  from  materials  containing  chromic  oxide,  ap- 
peared in  1899  in  the  Zeitschrift  fur  angewandte  Chemie* 
After  a  short  review  of  all  the  previously  proposed  processes 
for  the  manufacture  of  chromic  acid,  Regelsberger  described 
some  investigations  he  himself  had  made  on  the  electrolytic 
regeneration  of  chromic  acid. 

^e  first  thought  to  oxidize  solid  residues  containing  chromic 
oxiuc  in  an  alkaline  solution,  by  the  oxidizing  influence  of 
chloride  of  calcium,  similarly  to  what  Dercum2  had  done  for 
the  chromium  solutions.  The  results  were  unfavorable,  and  it 
appeared  advisable  to  combine  the.  formation  of  the  oxidation 
reagents  (of  the  chloride  of  lime)  and  the  regeneration  of  the 
chromic  acid  in  one  process,  so  a  solution  of  chloride  was 
electrolyzed  ?  an  auxiliary  electrolyte,  and  in  this  solution 
chromium  h  oxide  was  slowly  introduced.  With  a  suffi- 
ciently lon^  sSage  of  the  current  he  found  that  a  complete 
transformation  into  chromate  of  the  added  chromic  oxide  had 
taken  place,  while  a  corresponding  oxidation  was  not  to  be 
detected  when  using  --.1kaline  sulphates ;  the  reaction  only 
began  c  >r  the  addition  of  a  certain  amount  of  chloride. 

By  the-'addition  of  chromic"  chloride  alone  only  chlorine  and 
metallic  Chromium  resulted  ;  but  on  the  addition  of  a  larger 
amount  of  chloride  oxid^tlfvn^tQ  chromic  acid  began. 

From  this  was  crutful,  unless  l^Lrin  the  best  current  out- 
put^ .;•*  much  clrsually  present  a  sim§,  continuously  dissolved 
i  almost .- ,  it  might  be  used  in  s£  .ine  chlorides  in  amount 
equal  to  th/e  chromium  resi^nes  a'  given  time  interval,  in 

1  Page  i:r  the  purpose  or 

2  Engli:out  of     the    S0-b-  T5,  1898. 


106  CHROMIUM  AND  ITS  COMPOUNDS. 

doing  which  naturally  the  chromic  oxide  must  be  well  dis- 
tributed." 

The  oxidation  product  was  principally  bichromate  and  may 
be  allowed  to  accumulate  in  the  solution  without  decreasing 
greatly  the  current  output,  although  doing  so  perceptibly. 
By  the  use  of  KC1  as  the  auxiliary  electrolyte,  potassium  bi- 
chromate can  be  finally  crystallized  out  in  the  purest  form 
from  the  hot  solution,  while  in  the  case  of  the  sodium  bichro- 
mate solution  the  largest  part  of  sodium  chloride  must  be  pre- 
viously removed  by  evaporation. 

By  not  quite  clear  theoretical  considerations,  Regelsberger 
attempts  then  to  prove  "that  with  equal  returns  in  formation 
of  chromate  the  highest  current  consumption  (in  ampere 
hours)  takes  place  when  using  a  chromic  salt,  a  considerably 
smaller  (4/7  of  the  first)  by  the  use  of  chromium  hydroxide, 
and  the  smallest  (3/7  of  the  first)  by  the  presence  of  a  quan- 
tity of  base  equivalent  to  the  bichromate  solution." 

In  relation  to  the  method  of  procedure,  a  diaphragm  is  not 
necessary.  For  larger  experiments  (40  amperes  and  over)  a 
rectangular  metal  box  was  used,  whose  under  part  was  roof- 
shaped  and  fastened  with  a  flange  to  the  upper  part,  which 
is  lined  inside  with  vulcanized  rubber.  The  lower  part 
serves  as  a  cathode,  opposite  to  which  a  roof-shaped  anode  of 
platinum  netting  hangs.  Air  is  blown  in  to  increase  the  cir- 
culation. For  small  experiments  the  following  apparatus 
serves :  two  vertical  platinum  electrodes  in  a  glass  vessel.  No 
other  suitable  anode  material  than  platinum  has  been  found  ; 
PbO2  has  too  low  a  conductivity,  and  carbon  is  too  strongly 
attacked.  The  results  of  the  experiments  are  given  as  fol- 
lows: 

(i).  400  ccm.  of  saturate. ri  of  chromilution  -f-  100  grams  of 
NaCl  was  diluted  to  450  ccmy  an  elect-- -Jyi.  of  chrome  alum 
solution  containing  4.20  gra  on  of  a  c  2O3«iiic  s  slowly  added. 
12.84  ampere-hours  applied.  >n.lplr  )mot*  sulphce  3.55  volts 
at  49°  to  66°,  and  electrodes  15  U3;  identic?-*  With  -.'rent  density 
at  the  anode,  which  had  24  square  £lanc  a>  t^eisen^face,  0.178 


OXYGEN    COMPOUNDS.  107 

ampere  per  square  centimeter,  on  the  cathode  with  94  square 
centimeters  surface,  0.0454  ampere.  The  current  output  of 
K2Cr2O7  was  34.2  per  cent.  Almost  all  the  CrzO3  was  used  up. 

2.  200  cc.  of  a  25  per  cent,  solution  of  KC1  with  a  gradual 
addition  of  62.6  cc.  of  neutral   chrome  alum  solution,  con- 
taining 1.9   grams  of  Cr2O3.     5.6  ampere-hours  applied.     A 
dark  brown  flocculent  precipitate  came  down  first,  and  all  ex- 
cept a  few  flakes  disappeared  ;  there  was  no  Cr2O3  present  at 
the  end.     The  current  output  of  K2Cr2O?  corresponded  to  36 
per  cent. 

3.  25  per  cent.  KC1  solution  —  gradual  addition  of  chromic 
chloride  solution  (from   100  grams  of  chromic  hydroxide  = 
50  grams  Cr2O3  dissolved  in  HC1   and  neutralized  as  far  as 
possible  by  repeated   evaporations).     32.5    ampere-hours.     4 
volts  at  60°.     The  current  output  of  K2Cr2O7  represented  35 
per  cent.  ;  nearly  half  had  crystallized  out. 

4.  25  per  cent,  solution  of   KC1,  to  which  was  gradually 
added  50  grams  of  chromic  hydroxide  which  had  been  pre- 
cipitated with  21  grams  of  caustic  lime.     29.5  ampere-hours. 
Anode  current  density  0.754  ampere  per  square  centimeter, 
4.45  volts  at  48°.     Current  output  of  K2CraO7  61.9  per  cent. 
A  part  had  crystallized  out. 

5.  Saturated  NaCl  solution  —  to  which  was  added  a  solu- 
tion of  50  grams  of  chromium  hydroxide  and  12. 75  grams  of 
NaOH.     36   ampere-hours.     Anode    current    density    0.692 
ampere  per  square  centimeter,  5.2  volts  at  78°.     63  per  cent, 
output.     In  the  last  two  cases,  the  formation  of  a  dark  brown 
precipitate   consisting   of   Cr2O3   and    CrO3  was  particularly 
noticeable. 

In  reference  to  the  practical  application  of  the  method,  I 
will  say  that  it  is  doubtful,  unless  the  oxidation  in  an  acid 
solution  does  not  usually  present  a  simpler  method  of  proce- 
dure. However,  it  might  be  used  in  some  special  cases,  for 
instance,  if  the  chromium  residues  are  available  in  the  solid 
form  or  if  for  the  purpose'  of  purifying,  a  precipitation  of  the 
chromium  out  of  the  solution  as  chromic  oxide  is  to  be 


108  CHROMIUM  AND  ITS  COMPOUNDS. 

recommended.  The  case  may  also  be  imagined  where  the 
oxidation  of  the  alkaline  electrolyte  would  follow  advan- 
tageously the  ignition  of  chromic  oxide  with  lime  as  an 
auxiliary  operation. 

On  the  whole  it  can  be  said  that  the  outlook  for  the  prac- 
tical application  of  the  alkaline  oxidation,  even  with  cheap 
electrical  energy  is  at  present,  very  limited. 

For  performing  the  oxidation  in  acid  solution,  Regelsberger 
first  used  only  platinum  anodes  and  even  had  little  success 
with  the  use  of  a  diaphragm.  He  first  obtained  satisfactory 
results  in  a  sulphuric  acid  solution  by  the  use  of  lead  anodes. 
According  to  Elbs1  a  70  per  cent,  current  efficiency  could  be 
obtained  by  the  use  of  freshly  ignited  platinum  anodes  and  a 
low  current  density.  The  application  of  electrolysis,  relative 
to  economy  of  voltage,  should  occur  in  warm  solutions  ;  also 
raising  of  the  temperature  seems  to  have  a  good  influence  on 
the  current  output  itself.  The  alternation  of  the  cathode  and 
anode  solutions  as  in  the  patent  of  Hochst  Color  Works  (see 
page  104)  is  emphasized  as  practical.  An  addition  of  iron  to 
the  solution  must  be  avoided,  as  it  causes  a  loss  of  current, 
which  at  least  would  not  be  the  case  if  the  iron  possessed  an 
oxidizing  effect  in  the  application  of  the  oxidized  solution. 

The  output  with  the  application  of  a  pure  chrome  alum 
solution  with  or  without  free  sulphuric  acid  for  the  electro- 
lyte, went  up  to  92.5  per  cent.,  70  per  cent,  of  the  added 
amount  being  oxidized,  and  with  80  to  86  per  cent,  efficiency 
of  oxidation.  The  chrome  alum  solution  used  carried  about 
30  grams  of  Cr2O3  per  liter. 

As  soon  as  the  larger  part  of  the  chromium  was  oxidized, 
there  occurred  a  strong  evolution  of  oxygen,  this  serving  as  a 
sign  for  the  renewal  of  the  solution  or  a  more  active  circu- 
lation. 

With  each  electrolysis  there  formed  a  small  amount  of  a 
yellowish  white  slime,  composed  of. lead  sulphate  and  lead 
chromate,  and  a  brownish  coat  on  the  anode,  which  scarcely 

1  Zeitschr.  f.  Elektrochemie,  6,  388  (1900). 


OXYGEN   COMPOUNDS.  1 09 

influenced  the  electromotive  force,  since  it  was  easily  shaken 
off. 

With  an  anode  current  density  of  0.065  to  o.ojo  ampere  per 
square  centimeter,  a  somewhat  higher  cathode  density,  and  a 
total  current  of  42  amperes,  three  volts  tension  was  used,  tem- 
perature 75°  ;  to  use  this  voltage  at  30°  temperature,  not  over 
0.03  ampere  per  square  centimeter  could  be  exceeded.  The 
apparatus  consisted  of  a  lead  box.  In  the  box  is  found  the 
diaphragms,  and  the  cathodes  of  any  suitable  conducting  mate- 
rial. The  anode  may  be  either  the  lead  box,  or  may  consist  of 
perforated  lead  plates  surrounding  the  diaphragms. 

The  power  consumption  may  be  reckoned  as  8  to  n  kilo- 
watts for  each  100  kilograms  of  Na2Cr2Oy  produced  per  24 
hours.  To  this  must  be  added  the  cost  of  the  simple  appara- 
tus, the  diaphragms  being  the  chief  consideration  according  to 
Regelsberger,  but  which  is  not  the  case  at  present,  and  finally 
the  regulation  of  the  apparatus,  which  may  be  assumed  for 
the  most  part  simple  and  automatic.  "It  is  therefore 
very  apparent  that  the  cost  of  the  regeneration  of  100  kilo- 
grams of  Na2Cr2CT  should  not  be  over  $5.00.  Of  course  cheap 
electrical  energy  is  assumed.  Regelsberger  compares  this 
cost  of  $5.00  with  the  commercial  value  of  100  kilograms  of 
bichromate,  worth  at  present  $13.50,  not  counting  in  the  last 
the  required  amount  of  sulphuric  acid  to  start  the  oxidizing 
action  which  up  to  the  present  was  always  lost.'' 

The  comparison  would  have  been  more  exact  if  made  with 
the  former  regeneration  cost,  which  did  not  amount  in  toto  to 
more  than  $5.00. 

Regelsberger  closes  with  the  words  : 

"  The  process  for  the  'oxidation  in  acid  solutions'  will 
doubtless  be  of  great  importance,  as  soon  as  the  question  of 
diaphragms,  which  to-day  is  a  serious  problem  in  the  electro- 
chemical industry,  has  been  satisfactorily  solved,"  etc. 

A  little  later  there  came  into  general  notice,  a  patent1  of 

1  German  Patent  109,012.  January  13,  1897.     Identical  with  the  Austrian 
patent  5658,  of  v.  Erggelet,  dated  April  19,  1901. 


110  CHROMIUM  AND  ITS  COMPOUNDS. 

Darmstadter's,  which  apparently  solves  the  problem  of  the  re- 
generation of  chromic  acid  in  a  highly  simple  and  elegant 
manner.  Darmstadter  puts  the  substance  to  be  oxidized  into  a 
solution,  for  instance,  of  chromium  sulphate  in  sulphuric  acid, 
and  electrolyzes.  "  In  case  there  is  sufficient  circulation 
every  trace  of  chromic  acid  formed  must  immediately  be  oxi- 
dized ;  an  accumulation  of  it  is  not  possible,  and  therefore 
any  too  strong  action  impossible,"  which  in  the  usual  oxida- 
tion methods  leads  easily  to  a  combustion  of  the  substance 
being  oxidized. 

In  this  way  chinon  can  easily  be  prepared  from  aniline  ; 
this  latter  compound  is  brought  directly  into  the  cold  bath, 
consisting  of  chromium  sulphate  and  sulphuric  acid,  and 
electrolyzed  with  continual  stirring.  The  change  takes  place 
without  noticeable  loss. 

In  an  analogous  manner  acetic  aldehyde  may  be  prepared 
from  ethyl  alcohol. 

Also  the  process  is  said  to  be  particularly  advantageous  for 
the  oxidation  of  anthracene  or  naphthaline .;  these  materials 
are  put  without  further  precautions  into  the  chromium  solu- 
tion acidified  with  sulphuric  acid,  and  electrolyzed  with  good 
circulation.  "  There  results  a  good  output  of  phthalic  acid 
or  anthrachinone." 

In  the  same  manner  the  most  varied  other  soluble  or  insolu- 
ble organic  compounds  may  be  oxidized. 

The  high  current  output  of  this  process  is  a  further  advan- 
tage. If  chromic  sulphate  is  oxidized  in  acid  solutions  with- 
out simultaneously  introducing  reducing  substances,  the  cur- 
rent output  decreases  the  more  chromic  acid  there  is  formed.  It 
is  quite  otherwise  with  the  process  in  question  ;  an  almost  quan- 
titative current  output  is  here  obtained.  "  Since  in  this  case 
every  trace  of  chromic  acid  is  changed  instantly  back  into 
chromic  sulphate  there  is  always  a  large  excess  of  the  latter 
present  whereby  the  electrolytically  produced  oxygen  is  very 
completely  utilized." 


OXYGEN   COMPOUNDS.  Ill 

Diaphragms  are — according  to  the  patent  specification  — 
not  necessary,  because  the  chromic  acid  is  utilized  immedi- 
ately after  its  production  for  oxidation  and  no  trace  reaches 
the  cathode.  A.  diaphragm  is  used  only  in  such  cases  where 
the  organic  oxidation  product  is  decomposed  by  the  cathodic 
hydrogen. 

It  is  at  times  used  when  producing  insoluble  materials  in 
order  to  hinder  a  deposition  upon  the  electrodes,  being  placed 
in  a  particular  part  of  the  electrolytic  bath  which  itself  is 
separated  from  the  electrode  space  by  a  filter  cloth  or  the 
like. 

The  substance  to  be  oxidized  can  be  put  in  a  separate  ves- 
sel, which  must  be  in  direct  and  continual  communication 
with  the  electrolytic  bath,  between  which  as  above  a  piece 
of  filter  cloth  is  interposed. 

In  relation  to  the  details  of  operation,  is  appended  :  "  When 
the  oxidation  of  the  organic  material  and  the  regeneration  of 
the  chromium  solution  takes  place  in  separate  vessels,  the 
solutions  employed  should  be  as  concentrated  in  chromic 
oxide  as  possible,  containing  10  to  12  per  cent,  or  more 
thereof,  so  that  it  will  be  seldom  necessary  to  transfer  the 
heavy  solution  from  the  electrolytic  bath  to  the  oxidation  ves- 
sel, and  to  perform  other  heavy  operations  as  infrequently  as 
possible.  With  the  process  in  question  this  is  for  evident 
reasons  not  necessary,  and  it  suffices  completely  if  the  solu- 
tion contains  4  to  5  per  cent,  of  chromic  oxide  or  less.  The 
content  of  sulphuric  acid  is  made  high  —  20  to  25  per  cent.  — 
in  order  to  increase  the  conductivity  of  the  electrolyte." 

u  The  current  density  may  vary  within  wide  limits  for  an 
equally  good  output  is  obtained  with  currents  from  0.005  to 
0.05  and  even  higher  ampere  per  square  centimeter."  The 
electromotive  force  varies  between  2.5  and  4  volts. 

Patent  Claim. 

i.  Process  for  the  oxidation  of  organic  substances  by  means 
of  chromic  acid,  characterized  by  the  reactions  taking  place 


112  CHROMIUM  AND  ITS  COMPOUNDS. 

in  the  electrolytic  bath,  in  such  manner  that  the  reduction 
pioduct  of  the  chromic  acid  is  continually  re-transformed  into 
chromic  acid  by  the  action  of  the  electric  current. 

2.  A  manner  of  carrying  out  the  process  of  oxidation  pro- 
tected by  claim  i,  consisting  in  treating  the  organic  substance 
to  be  oxidized,  in  a  part  of  the  cell  separated  from   the  elec- 
trode compartment  by  a  sieve  or  filter  cloth. 

3.  A   manner  of  carrying  out  the  oxidation  process  pro- 
tected in  claims  i  and  2,  consisting  in  bringing  the  substance 
to  be   oxidized  in  a  separate  vessel  whose  contents  are  in 
direct  communication  with  the  contents  of  the  bath,   instead 
of  in  a  part  of  the  bath  partitioned  off. 

I  have  already  given  a  criticism  of  the  preceding  process  in 
a  lecture  entitled  :  u  The  Electrolytic  Regeneration  of  Chromic 
Acid  and  the  Production  of  Acid  Resisting  Diaphragms."  * 
I  said  therein:  "He  (Darmstadter)  takes  the  point  of  view, 
that  the  chromic  acid  yields  its  oxygen  up  immediately  to  the 
substance  to  be  oxidized,  so  that  the  reducing  action  of  the 
cathode  does  not  enter  into  the  question,  and  the  oxidized 
substance  itself  is  little  or  not  changed  by  the  cathode.  Aside 
from  the  latter  assumption  we  must  on  the  grounds  of  ex- 
perience also  regard  this  process  as  very  little  hopeful,  since 
the  action  of  the  oxidizing  agent  on  organic  substances  is  in 
general  not  instantaneous,  and  from  previous  investigations 
(see  further  on)  on  the  great  facility  of  reduction  of  the 
chromic  acid.  On  reading  the  patent  specification,  it  might 
be  believed,  that  the  problem  is  simply  solved  when  he 
speaks  of  the  obtaining  of  a  practicable  output  of  phtalic 
acid  or  anthrachinone,  from  the  oxidation  of  respectively 
napthaline  and  anthracene.  According  to  our  investigations 
the  process  is  not  applicable  for  the  direct  production  of  just 
these  materials;  we  have  not  once  been  able  to  prove  the 
formation  of  phtalic  acid  qualitatively,  with  assurance. 

The  following  experiments  had  for  their  object  the  settling 
of  the  question  as  to  whether  it  was  promising  to  work  with- 
1  Zeitschr.  f.  Elektrochemie,  7,  290  (1900). 


OXYGEN    COMPOUNDS.  1 13 

out  diaphragms.  If  the  chromium  sulphate  solution  acidified 
with  sulphuric  acid  is  electrolyzed  without 'diaphragms,  an 
oxidizing  action  of  the  current  is  noticed,  Liout  the  output  is 
very  unsatisfactory.  There  was  obtained  in"  an  investigation 
with  a  sulphuric  acid  solution  containing  100  grams  of 
chromic  oxide  per  liter  and  using  0.03  amjjere  per  square  cen- 
timeter and  lead  electrodes,  at  ordinary  temperatures,  a  cur- 
rent output  of  less  than  10  per  cent,  for  the  solution  contained 
at  the  end  of  the  investigation  about  6  grams  of  chromic 
acid  per  liter,  and  this  large  loss  in  spite  of  the  small  concen- 
tration of  the  chromic  acid  formed.  If  the  current  density  at 
the  cathode  is  raised,  a  larger  output  is  obtained  with  a 
simultaneous  increase  of  voltage  ;  but  a  practical  application 
of  the  process  is  not  to  be  thought  of.  Changing  the  mate- 
rial of  the  cathode  had  no  beneficial  effect. 

In  reference  to  the  process1 6f  FitzGerald  (page  95)  for  the 
simultaneous  separation  of  2ihc  and  chromic  acid,  I  should 
say:  Theoretically  such  'a  'combination  of  double  working 
appears  pretty,  and  it  pefhaps1  directs  the  attention  to  making 
such  combinations  in  m&hy  electrolytic  processes;  we  have 
it  also  in  the  decomposition  of  the1  alkaline  chlorides,  but  here 
it  lies  in  the  nature  of  the  operation.  In  practice  such  an 
artificial  combination  cannot  often  be  arranged,  since  for 
practical  use  there  is  always  the  danger  that  in  obtaining  one 
material  the  other  must  always  be'  produced,  even  when  its 
production  is  unprofitable.  In  such  changeable  combinations 
great  precautions  must  be  taken  in  their  installation. 

The  proposition  of  FitzGerald  is  naturally  unusable  in  the 
electrolytic  regeneration  of  chromium  on  a  large  scale  ;  since 
where  would  the  large  quantity  of  zinc  sulphate  come  from? 
It  is  not  a  long  step,  however,  to  replace  the  zinc  sulphate 
solution  by  sulphuric  acid.  If  we  'do  this  we  quickly  observe 
an  enrichment  in  sulphuric  acid  at  the  anode  side 'and  an  im- 
poverishment at  the  cathode  side.  It  would  therefore  'be 
necessary  in  this  process  to  precipitate  the  excess^of  sulphuric 
acid  out  of  the  chromium  solution- from  time  to  time 'by  lime 


114  CHROMIUM    AND    ITS    COMPOUNDS. 

and  to  replace  by  fresh  concentrated  acid  the  dilute  sulphuric 
acid  on  the  cathode  side,  which  is  contaminated  by  the  chro- 
mium which  has  diffused  over. 

I  spoke  further  in  the  lecture  quoted  of  the  German  patent 
103,860  (see  page  104)  invented  by  me  and  belonging  to  the 
Hochst  Color  Works  ;  and  will  make  some  further  remarks  : 
The  current  output  is  principally  dependent  upon  the  per- 
centage of  chromic  oxide  in  solution  and  how  far  it  is  to  be 
oxidized,  as  well  as  on  the  quantity  of  organic  substances  in 
the  solution  and  how  far  it  must  be  burned  by  the  oxidizing 
action  of  the  current,  and  finally  on  the  properties  of  the 
electrodes  and  the  temperature.  In  general  70  to  90  per  cent, 
output  can  be  counted  on,  on  a  large  scale.  The  tension 
changes  with  the  conductivity  of  the  solution  used,  the  cur- 
rent density,  the  distance  of  the  electrodes  apart,  the  temper- 
ature of  the  solution  and  the  thickness  of  the  diaphragms 
used.  If  one  has,  for  instance,  cheap  electrical  power  no  par- 
ticular value  would  attach  to  the  least  possible  working  ten- 
sion, but  other  considerations  would  be  of  first  importance  in 
obtaining  the  best  commercial  result.  Usually  the  tension  is 
held  between  2.7  and  4  volts. 

Only  lead  anodes  are  used,  which  quickly,  cover  themselves 
with  a  layer  of  peroxide.  According  to  Regelsberger  (see 
page  106)  the  output  is  considerably  larger  with  lead  electrodes 
than  with  platinum,  which  is  to  be  ascribed  to  the  over- 
voltage,  which  must  be  used  to  evolve  hydrogen  on  the  per- 
oxidized  plates  and  which  thus  allows  of  the  conversion  of 
trivalent  chromium  ions  into  the  hexavalent,  without  free 
oxygen  escaping  in  considerable  amount. 

Another  way  is  perhaps  worth  mentioning  by  which  chro- 
mium solutions  are  oxidized,  although  it  has  not  proven  itself 
of  practical  value.  Lead  peroxide  oxidizes  chromic  oxide  to 
chromate,  and  a  charged  accumulator  plate  placed  in  chromic 
sulphate  solution  discharges  itself  spontaneously,  oxidizing 
the  solution.  The  discharged  plate  can  now  be  put  into 
storage-battery  sulphuric  acid,  and  charged,  using  a  lead  plate 


OXYGEN   COMPOUNDS.  115 

as  cathode.  By  allowing  the  plate  to  alternately  discharge  in 
the  chromic  solution  and  be  recharged  in  sulphuric  acid,  the 
putting  in  of  a  diaphragm  is  unnecessary,  and  the  oxidation 
may  be  done  with  a  low  tension.  Unfortunately  the  plate 
gives  out  quickly. 

Summing  up,  I  remarked  that  a  rational  process  for  the  elec- 
trolytic regeneration  of  chromic  acid  without  a  diaphragm  did 
not  exist.  We  are  therefore  restricted  to  them  and  will  con- 
sider finally  the  attempts  which  led  me  to  the  production  of  a 
good  and  cheap  diaphragm. 

Lastly  concerning  the  cost,  an  average  of  350  kilowatt-hours 
will  produce  100  kilograms  of  CrO3  in  solution  from  chromic 
oxide,  according  to  the  data  given.  In  conclusion  I  refer  to 
the  data  of  Regelsberger  (page  109),  in  which  it  perhaps  might 
be  remarked  that  the  hope  is  entertained  that  the  partial  ac- 
cumulation of  a  sinking  fund  would  materially  reduce  the 
cost. 

A  short  time  after  this  lecture,  Darmstadter  published  a 
second  process1  for  the  regeneration  of  chromic  acid.  He 
mentions  the  process  protected  by  the  German  Patent 
103,860  (page  104),  and  believes  that  the  difficulties  there 
avoided  by  the  changing  of  the  anode  and  cathode  solutions 
could  be  avoided  by  taking  into  consideration  ordinary  hydro- 
diffusion. 

The  sulphuric  acid  formed  in  the  cathode  space  by  the  elec- 
trolysis as  well  as  that  formed  by  the  oxidation  of  the  chromic 
sulphate  tends  to  distribute  itself  equally  in  both  compart- 
ments, and  therefore  to  act  against  the  accumulation  of  the 
acid  in  the  cathode  compartment.  Likewise  the  chromic 
sulphate,  which,  for  like  reasons,  accumulates  in  the  cathode 
space  and  decreases  in  the  anode  space,  tends  by  diffusion  to 
become  of  equal  concentration  in  both  spaces.  If  now  the 
current  density  is  so  regulated  that  the  transference  of  the 
sulphuric  acid  as  well  as  the  chromic  sulphate  in  the  one 
direction  is  compensated  by  the  transference  in  the  other 

1  German  Patent  117,947,  Nov.  3,  1899. 


1 1 6  CHROMIUM  AND  ITS  COMPOUNDS. 

direction,  one  has  a  simple  means  at  hand  for  overcoming  the 
aforesaid  difficulties  without  it  being  necessary  to  frequently 
renew  the  solution  in  the  cathode  compartment. 

As  the  velocity  of  hydro-diffusion  is  dependent  on  the 
difference  of  concentration,  and  on  the  surface  and  penetra- 
bility of  the  diaphragm,  so  is  (I  remark  further  according 
to  the  specifications)  the  current  density  regulated  to  these 
conditions,  that  is  it  may  be  so  much  the  greater,  the  greater 
the  diaphragm  surface  and  the  greater  the  differences  of  con- 
•centration  of  the  sulphuric  acid  and  chromic  sulphate  in  the 
two  compartments.  The  current  strength  corresponds  to  the 
changes  in  the  latter  during  the  electrolysis. 

If  changes  in  concentration  occur  during  the  electrolysis, 
that  do  not  injure  anything,  they  must  after  ending  be 
equalized. 

Under  certain  conditions  it  is  practicable  to  so  operate  the 
process  that  one  constituent  maintains  its  concentration  con- 
stant, while  that  of  the  other  changes. 

If  the  highest  allowable  current  densities  are  to  be  em- 
ployed then  care  must  be  taken  to  keep  the  difference  in  con- 
centration very  large,  that  is  the  content  of  sulphuric  acid  in 
the  anode  compartment  very  high,  the  content  of  chromium 
sulphate  as  low  as  possible.  To  attain  this  with  continuous 
driving,  one  must  resort  to  the  addition  of  fresh  solution 
mixed  with  a  large  amount  of  solution  which  has  been  al- 
ready oxidized,  so  that  the  solution  in  the  anode  compartment 
is  always  to  a  great  extent  oxidized  and  contains  a  relatively 
large  quantity  of  free  sulphuric  acid  and  a  small  amount  of 
chromic  sulphate. 

If  the  solution  to  be  oxidized  is  passed  through  the  anode 
compartments  of  a  number  of  baths,  using  the  apparatus  in 
series,  then  it  is  recommended  that  a  smaller  current  density  — 
calculated  on  the  diaphragm  surface  —  should  be  used  in  the 
first  than  in  the  last. 

Patent  Claims. 

i.   Process  for  the  oxidation  of  acid  chromium  salt  solutions 


OXYGEN   COMPOUNDS.  117 

in  electrolytic  baths  with  diaphragms,  characterized  by  the 
regulation  of  the  current  density,  so  that  the  content  of  free 
acid  or  chromium  salt  or  both  in  the  cathode  space  during 
the  course  of  the  electrolysis,  is  not  appreciably  altered. 

2.  A  method  of  operating  the  process  of  claim   i,   wherein 
for  the  furtherance  of  the  therein  expressed  purpose,  the  addi- 
tion of  fresh  and  the  abstraction  of  oxidized  solution  is  so  reg- 
ulated that  in  the  anode  compartment  there  is  always  found 
a  solution  which  for  the  most  part  is  oxidized,  so  that  it  con- 
tains proportionately  a  large  quantity  of  free  acid  and  a  pro- 
portionately small  quantity  of  unoxidized  chromium  salt. 

3.  A  method  of  operating  the  process  of  claim   i,  whereby 
when  passing  the  solution  to  be  oxidized  through  a  series  of 
several  baths,  varying  current  densities  —  calculated  on  the 
diaphragm  surface  —  are  used  in  the  single  baths  for  the  at- 
taining of  the  desired  object. 

The  carrying  out  of  the  general  idea  mentioned  in  the  pre- 
ceding patent,  to  make  the  concentration  changes  through 
diffusion  occasioned  by  the  action  of  the  current  retrogressive, 
appears  hopeless  in  practice  because  the  velocity  of  diffusion 
is  so  small.  Above  all  things  it  must  be  mentioned  that  the 
application  of  this  idea  in  the  above  case,  seems  to  be  wholly 
out  of  place.  For  if  there  is  a  noticeable  diffusion  of  sulphuric 
acid  from  the  anode  into  the  cathode  compartment,  and  of 
chromic  sulphate  in  the  opposite  direction  chromic  acid 
formed  on  the  anode  side  will  wander  over  to  the  cathode 
side  where  its  concentration  is  almost  zero,  and  so  correspond- 
ingly diminish  the  output.  If  the  chromic  acid  concentra- 
tion on  the  anode  side  is  kept  as  high  as  possible  right  from 
the  beginning,  as  is  especially  recommended,  the  loss  will 
naturally  be  so  much  the  greater,  until  it  happens  that  the 
chromic  acid  formed  at  the  anode  becomes  so  much  smaller 
in  comparison  with  the  quantity  of  current  sent  through,  the 
more  chromic  acid  is  already  present.  On  the  whole  the 
process  must  be  characterized  as  impracticable. 

An   English  patent1  of  Schneider,  of  a  later  date  concerns 

1  English  Patent  19,029,  Oct.  24,  1900. 


Il8  CHROMIUM    AND    ITS   COMPOUNDS. 

itself  very  closely  with  the  contents  just  described  of  the  Ger- 
man patent  of  Darmstadter.  Schneider  also  uses  the  aid  of 
diffusion  in  order  to  make  the  diffusion  changes,  which  dur- 
ing the  electrolysis  of  chromium  solution  take  place  on  both 
sides  of  the  diaphragm,  again  retrogressive,  to  which  he  adds 
at  least  that  in  general  only  small  current  densities  may  be 
employed.  He  also  mentions  that  using  a  solution  contain- 
ing 100  grams  of  chromic  sulphate  and  100  grams  of  sulphuric 
acid  per  liter,  and  a  current  density  of  0.0025  to  0.0050  am- 
pere per  square  centimeter  (according  to  the  nature  of  the 
diaphragm)  no  change  of  concentration  of  sulphate  or  acid 
took  place  in  the  cathode  space  before  or  after  the  electrolysis ; 
also  working  with  0.03  ampere  current  density,  it  made  itself 
noticeable  and  it  could  therefore,  in  this  case  if  the  vessel 
stood  long  enough  without  current,  be  made  retrogressive. 

As  a  means  of  increasing  this  back  diffusion  it  is  recom- 
mended as  in  the  German  Patent  117,949,  to  use  only  such 
solutions  as  anode  electrolytes  which  are  already  in  the  greater 
part  oxidized,  and  according  to  that  regulate  the  addition  of 
new  solution  and  the  abstraction  of  old  in  the  anode  compart- 
ment, or  better  still  to  mix  the  anode  and  cathode  solutions. 
The  latter  could  be  done  in  this  manner,  by  allowing  fresh 
solution  to  run  into  the  electrolyzing  vessel  until  the  level  of 
the  fluid  stood  above  the  edge  of  the  diaphragm,  which  is 
usually  lower  than  the  edge  of  the  vessel,  thus  allowing  un- 
hindered diffusion  of  both  fluids,  which  finally  is  also  facili- 
tated by  stirring. 

The  practical  application  was  carried  out  in  the  following 
manner.  By  using  a  solution  containing  100  grams  of 
chromic  sulphate  and  50  grams  of  sulphuric  acid  per  liter, 
and  a  current  density  of  0.02  to  0.03  ampere  per  square  centi. 
meter,  it  is  found  that  after  about  half  of  the  chromic  sulphate 
had  been  oxidized  at  the  anode,  the  acid  concentration  at  the 
anode  had  risen  to  100  to  150  grams  per  liter,  and  a  corre- 
sponding fall  had  taken  place  at  the  cathode.  At  this  time 
enough  fresh  chromic  solution  was  put  into  the  vessel 


OXYGEN   COMPOUNDS.  119 

until  the  edge  of  the  diaphragm  was  covered,  when  a  mixture 
of  the  anode  and  cathode  fluids  will  take  place  in  several 
hours,  or  in  a  shorter  time  by  the  aid  of  stirring,  and  the  dif- 
ference of  concentration  will  be  equalized,  upon  which  the 
electrolysis  may  be  continued  after  the  removal  of  the  upper 
layer  of  solution. 

If  the  solution  contains  100,  150  or  more  grams  of  sulphuric 
acid  per  liter,  then  such  a  mixing  will  be  required  only  at 
longer  intervals,  because  the  content  of  sulphuric  acid  in  the 
cathode  solution  will  not  be  reduced  to  such  a  small  value  in 
so  short  a  time. 

The  electrolysis  of  sulphate  solutions  is  also  recommended 
because  of  the  possibility  of  using  lead  electrodes. 

The  patent  claim  reads  : 

1.  A  method  for   the   equalization   of    the   concentration 
changes  occurring  in  the  electrolysis  of  chromium  oxide  solu- 
tions acidified  by  sulphuric  acid,  when  a  diaphragm   is  used, 
consisting  in  mixing  the  anode  and  cathode  fluids,  either   by 
increasing  the  diffusion  through  the  diaphragm  in  relation  to 
the  action  of  the  electrolytic  migration  or  by  free  diffusion  or 
by  the  aid  of  artificial  means. 

2.  A  method  of  equalization  (as  above),  consisting  in  mix- 
ing the  solutions,  by  the  aid  of  diffusion  through  the  dia- 
phragms, and  increasing  this  diffusion  velocity  in  relation  to 
the  transfer  velocity  of  the  sulphuric  acid  by  a  regulation  of 
the  current  density,  essentially  as  described. 

3.  A  method  for  the  equalization  (as  above),  consisting  in 
mixing  the  solutions  by  the  help  of  diffusion   through  the 
diaphragm,  and  admitting  a  continuous  or  intermittent  stream 
of  new  solution  in   the  anode  compartment,   drawing  off   a 
corresponding  amount  of  old  solution,  essentially  as  described. 

4.  A  method  for  the  equalization  (as  above),  consisting  in 
mixing  the  solutions  by  the  aid  of  diffusion   through  a  dia- 
phragm, and  from  time  to  time  interrupting  the  electric  cur- 
rent. 


120  CHROMIUM    AND    ITS   COMPOUNDS. 

5.  A  method  for  the  equalization  (as  above),  consisting  in 
the  direct  mixture  of  the  solutions  of  both  compartments. 

6.  A  method   for  the  equalization  (as  above),  consisting  in 
directly  mixing  the  solutions,  by  allowing  fresh  solution  to 
flow  in  until  the  edge  of  the  diaphragm  is  covered,   allowing 
the  whole  to  stand  for  some  time,  and   then  drawing  off  a 
sufficient  amount  of  solution,  essentially  as  described. 

7.  A  method  for  the  equalization  (as  above),  consisting  in 
a  direct  mixing  of  the  solution,  while  stirring,  essentially  as 
described. 

In  passing  judgment  upon  this  last  process  the  following 
with  reference  to  page  105  is  added  :  If  there  occurs  a  mixing 
of  the  anode  and  cathode  fluids  in  any  way,  either  by  free  or 
limited  diffusion,  or  diffusion  facilitated  by  stirring,  there  re- 
sults under  all  conditions  —  under  the  assumption  that  an  in- 
fringement of  patent  103,860  (page  104)  is  to  be  avoided  —  a 
certain  amount  of  the  chromic  acid  formed  at  the  anode  going 
to  the  cathode,  where  according  to  the  investigations  men- 
tioned on  page  101,  it  is  again  reduced.  This  process  is  less 
valuable  than  that  of  patent  103,860. 

APPENDIX. 

1.  The  chromium  carbide  C2Cr  ,  described  on  page  66,  can 
also  be  made  according  to  a  contribution  of  Moissan1  by  heat- 
ing a  mixture  of  equal  parts  of  chromic  oxide  and  calcium 
carbide  (200  grams  was  taken)  in  an  electric  furnace  for  five 
minutes,  using  900  amperes  at  45  volts.     Moissan  found  as 
the  products  of  the  reaction,  a  metallic  regulus  covered  with 
crystalline  needles,  underneath  a  covering  of  melted  calcium 
carbide,  and  by  analysis  corresponding  to  the  above  formula, 
and  containing  traces  of  iron  and  calcium. 

2.  On  the  preparation  of  acid  lead   chromate  according  to 
the  process  of  Luckow  (page  89),  J.  Rontschewsky  remarks 
in  a  paper,2  that  the  production  of  the  lead  chromate  may  be 
combined  with  the  electrolytic  obtaining  of  zinc  in  one  process, 
if  a  diaphragm  is  employed. 

1  Compt.  rend.,  125,  841  (1897). 

'2  Zeitschr.  f.  Elektrochemie,  7,  29  ( 1900). 


INDEX  OF  AUTHORS. 


Aschermann 42,  43,  47 

Boehringer  &  Sons 74 

Bonnet 3,  TO,  u,  13,  16,  18 

Borchers 37,  54 

Browne 86 

Buff 81,  101 

Bullier 64 

Bunsen i,  2,  3,  23,  53,  76,  77 

Chaplet 67 

Cowper-Coles 19,  25 

Darmstadter t no.  112,  115,  118 

De  Chalmot 70 

Demmenie 39 

Dercum 105 

Deville 54 

Dollner '  ;" •  '. 50 

Dufau 82 

Elbs i 108 

Electro-Metallurgical  Co 19,  23,  59 

Erggelet,  von 109 

Fe*re*e 19,  25,  53,  76 

FitzGerald 95,  103,  113 

Fremy 54,  82 

Geuther 101 

Glaser,  F 75 

Glaser,  G 27 

Goldschmidt,  H 30,  51,  63 

Goldschmidt,  Th 46,  47,  49,  6 1 

Haussermann 98,  99,  101 

Heibling 56,  102 

Heroult  . 62 

Hittorf 29,  31,  39 

Hochst  Color  Works 104,  108,  114 

KoryschefF 39 

Krupp 34 

L,e  Blanc 104,  112 

Le  Chatelier 82 

Lorenz 102 

I/uckow 87,  88,  120 

Maronneau 72 


122  INDEX. 

M  oiler 19 

Moissan 35,  36,  37,  38,  54,  55,  57,  64,  66,  68,  70,  81,  82,  85,  120 

Merges lor 

Mourlot 72 

Neumann    ..'....        27,  30 

Ostwald      .    '    • 31,  100 

Parker 71 

Placet 3,  10,  u,  13,  16,  19,  25,  59,  63 

Reese  .    .        . 80,  101 

Regelsberger    . ,  .    ,    .    '.    .    '. 105,  106,  108,  109,  115 

Reisenegger 104 

Rontschewsky 120 

Schneider 117 

Smith   '. 97 

Societe"  d'£lectro-Chimie  . '..'.' 51 

Socie'te  Ge'ne'rale  de  Aciers  Fins 61 

Socie'te  Neo-Metallurgie  Marbeau,  Chaplet  &  Co  . 57 

Strameo 79 

Street   .    .    .    .    .    .    ....    .  ' ! ! 19,  78,  80 

Vautin 44,  47,  49,  61 

Verneuil 82 

Vielhomme , 62 

Villon 73 

Williams 66 

Wilson 32 

Zettel 70 


UNIVERSITY 


